docs(fix): revert prettier formatting on markdown files (#1612)

Prettier formatting our markdown files is causing bugs because of the
differences between Gatsby's parser and Prettier's. Also, Prettier
formats the inline code-blocks containing example CMS configs, but the
formatting it uses doesn't really make much sense or match the suggested
CMS config style.

It doesn't actually make much sense to format the docs anyway, since we
use the CMS itself to edit/generate them.

.prettierignore

@@ -1,3 +1,2 @@
 dist/
-bin/
-CHANGELOG.md
+bin/