[#32862] Removed // comments from bootstrap css.

The // comments are not intended to be present in the css files.  They are
only present in the .less files to identify changes from standard bootstrap.
Adding cy_GB (Welsh) language to installation
Add link to coding standards to contributing.md
Close #3593
Merge pull request #3584 from pjwiseman/32862

[#32862] Removed // comments from bootstrap css.