Fix missing script .sh extensions; add Docker build notes

Makefile

@@ -4,7 +4,7 @@ dep:
 	docker build -t fira:latest .
 
 build:
-	docker run --rm -v ${PWD}:/opt fira:latest ./script/build
+	docker run --rm -v ${PWD}:/opt fira:latest ./script/build.sh
 
 package:
-	./script/package
+	./script/package.sh

README.md

@@ -196,13 +196,23 @@ In case you want to alter FiraCode.glyphs and build OTF/TTF/WOFF files yourself,
 
 ```bash
 # install all required build tools
-./script/bootstrap
+./script/bootstrap_macos.sh
 
 # build the font files
-./script/build
+./script/build.sh
 
 # install OTFs to ~/Library/Fonts
-./script/install
+cp distr/otf/*.otf ~/Library/Fonts
+```
+
+Alternatively, you can build Fira Code using Docker:
+
+```bash
+# install dependencies in a container and build the font files
+make
+
+# package the font files from dist/ into a zip
+make package
 ```
 
 ### Credits

script/everything

@@ -2,8 +2,8 @@
 cd "`dirname $0`/.."
 
 ./script/check_widths
-# ./script/build_ttf
-./script/build_variable
-./script/build_woff
-./script/build_woff2
-./script/package
+# ./script/build_ttf.sh
+./script/build_variable.sh
+./script/build_woff.sh
+./script/build_woff2.sh
+./script/package.sh