.gitattributes: various readability improvements

... as well as adding documentation to make it more straight-forward to understand what the file does and why.

Author: jrfnl

.gitattributes

@@ -1,15 +1,24 @@
-.cspell.json export-ignore
-.gitattributes export-ignore
-.github/ export-ignore
-.gitignore export-ignore
-phpcs.xml.dist export-ignore
-phpstan.neon.dist export-ignore
-phpunit.xml.dist export-ignore
-scripts/ export-ignore
-src/Standards/**/Tests export-ignore
-tests/ export-ignore
+#
+# Exclude these files from release archives.
+# This will also make them unavailable when using Composer with `--prefer-dist`.
+# If you develop for this repo using Composer, use `--prefer-source`.
+# https://www.reddit.com/r/PHP/comments/2jzp6k/i_dont_need_your_tests_in_my_production/
+# https://blog.madewithlove.be/post/gitattributes/
+#
+.github/                export-ignore
+scripts/                export-ignore
+src/Standards/**/Tests/ export-ignore
+tests/                  export-ignore
+.cspell.json            export-ignore
+.gitattributes          export-ignore
+.gitignore              export-ignore
+phpcs.xml.dist          export-ignore
+phpstan.neon.dist       export-ignore
+phpunit.xml.dist        export-ignore
 
+#
 # Declare files that should always have CRLF line endings on checkout.
+#
 *WinTest.inc text eol=crlf
 *WinTest.php text eol=crlf
 src/Standards/Generic/Tests/Files/LineEndingsUnitTest*.inc text eol=crlf