Update Linux install text

Simplify text, use title-caps
[ci skip]

doc/how_to_build_linux.md

@@ -2,41 +2,42 @@
 
 ## Required software
 
-You will need to install some dependencies before you can build. Depending on your distribution you will be able to install the packages directly with the command lines below or will have to manually install:
+Building OpenToonz from source requires the following dependencies:
 - Git
 - GCC or Clang
-- CMake
-  - confirmed to work with 3.4.1 and newer.
-- Qt5
-  - http://download.qt.io/official_releases/qt/5.5/5.5.1/
-- Boost
-  - http://www.boost.org/users/history/version_1_55_0.html
+- CMake (3.4.1 or newer).
+- Qt5 (5.5 or newer)
+- Boost (1.55 or newer)
 - SDL2
+- LibPNG
+- SuperLU
+- Lzo2
+- FreeType
 
-### Installing required packages on Debian / Ubuntu
+### Installing Dependencies on Debian / Ubuntu
 
 ```
 $ sudo apt-get install build-essential git cmake pkg-config libboost-all-dev qt5-default qtbase5-dev libqt5svg5-dev qtscript5-dev qttools5-dev qttools5-dev-tools libqt5opengl5-dev qtmultimedia5-dev libsuperlu-dev liblz4-dev libusb-1.0-0-dev liblzo2-dev libpng-dev libjpeg-dev libglew-dev freeglut3-dev libsdl2-dev libfreetype6-dev
 ```
 
 Notes:
-* It's possible we also need libgsl2 (or maybe libopenblas-dev)
+* It's possible we also need `libgsl2` (or maybe `libopenblas-dev`)
 
-### Installing required packages on RedHat / CentOS
+### Installing Dependencies on RedHat / CentOS
 
 TODO
 ```
 $ rpm ...
 ```
 
-### Installing required packages on Fedora
+### Installing Dependencies on Fedora
 (it may include some useless packages)
 
 ```
 $ dnf install gcc gcc-c++ automake git cmake boost boost-devel SuperLU SuperLU-devel lz4-devel lzma libusb-devel lzo-devel libjpeg-turbo-devel libGLEW glew-devel freeglut-devel freeglut SDL2 SDL2-devel freetype-devel libpng-devel qt5-qtbase-devel qt5-qtsvg qt5-qtsvg-devel qt5-qtscript qt5-qtscript-devel qt5-qttools qt5-qttools-devel qt5-qtmultimedia-devel blas blas-devel
 ```
 
-### Installing required packages on ArchLinux
+### Installing Dependencies on ArchLinux
 
 ```
 $ sudo pacman -S base-devel git cmake boost boost-libs qt5-base qt5-svg qt5-script qt5-tools qt5-multimedia lz4 libusb lzo libjpeg-turbo glew freeglut sdl2 freetype2
@@ -48,9 +49,9 @@ $ yaourt -S superlu
 ```
 
 Notes:
-* ArchLinux had BLAS split into blas and cblas
+* ArchLinux has `blas` split into `blas` and `cblas`.
 
-### Installing required packages on openSUSE
+### Installing Dependencies on openSUSE
 
 ```
 $ zypper in boost-devel cmake freeglut-devel freetype2-devel gcc-c++ glew-devel libQt5OpenGL-devel libSDL2-devel libjpeg-devel liblz4-devel libpng16-compat-devel libqt5-linguist-devel libqt5-qtbase-devel libqt5-qtmultimedia-devel libqt5-qtscript-devel libqt5-qtsvg-devel libtiff-devel libusb-devel lzo-devel openblas-devel pkgconfig sed superlu-devel zlib-devel
@@ -58,28 +59,30 @@ $ zypper in boost-devel cmake freeglut-devel freetype2-devel gcc-c++ glew-devel
 
 ## Build instructions
 
-### cloning the git tree
+### Cloning the GIT Tree
 
 ```
 $ git clone https://github.com/opentoonz/opentoonz
 ```
 
-### Copying the stuff directory
+### Copying the 'stuff' Directory
 
 TODO: some parts should really be installed in $prefix/ instead... and some other in various cache or user-local places.
 cf. https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
 Until then we just follow the Win32/OSX layout.
 
-It is supposedly optional but some files are actually required to run the executable properly.
+The `~/.config/OpenToonz/` directory contains your settings, work and other files.
 
-The .config/OpenToonz/ directory in your home folder will contain your settings, work and other files. We need to create it from the command-line:
+Initialize this path with the folling commands:
 
 ```
 $ mkdir -p $HOME/.config/OpenToonz
 $ cp -r opentoonz/stuff $HOME/.config/OpenToonz/
 ```
 
-### Creating a default ini file for stuff folders
+*Currently this is required to run OpenToonz.*
+
+### Creating SystemVar.ini
 
 TODO: fix the code to discover it automatically
 
@@ -98,9 +101,9 @@ TOONZROOT="$HOME/.config/OpenToonz/stuff"
 TOONZSTUDIOPALETTE="$HOME/.config/OpenToonz/stuff/projects/studiopalette"
 EOF
 ```
-Note the generated file must not actually contain "$HOME", this shell command repaces it with /home/youraccount in the generated file.
+Note the generated file must not actually contain `$HOME`, this expands to an absolute path in the generated file.
 
-### Building the tiff library from thirdparty
+### Building LibTIFF
 
 TODO: make sure we can use the system libtiff instead and remove this section.
 Features from the modified libtiff and needed currently, so this isn't a simple switch.
@@ -118,7 +121,7 @@ try appending `--disable-jbig` to the `./configure` command above and make clean
 This workaround means you won't be able to load images using this compression method
 (see https://github.com/opentoonz/opentoonz/issues/901) for updates on this issue.
 
-### Compiling the actual application
+### Building OpenToonz
 
 ```
 $ cd ../../toonz
@@ -130,18 +133,18 @@ $ make
 
 The build takes a lot of time, be patient.
 
-### Debugging the build
+### Troubleshooting Build Errors
 
 If something doesn't compile or link, please run `make` this way to help spot the problem:
 ```
 $ LANG=C make VERBOSE=1
 ```
 
-#### Debug build
+#### Debug Build
 If you need to debug the application, you should be able to use `cmake -DCMAKE_BUILD_TYPE=Debug`.
 
 
-### Running the application
+### Running OpenToonz
 
 You can now run the application:
 
@@ -150,7 +153,7 @@ $ cd bin
 $ LD_LIBRARY_PATH=./lib/opentoonz:$LD_LIBRARY_PATH ./bin/OpenToonz_1.0
 ```
 
-### Performing a system installation
+### Performing a System Installation
 
 The steps above show how to run OpenToonz from the build directory,
 however you may wish to install OpenToonz onto your system.