update Galaxy wiki page on github ansible community

Problem Description: update this page https://github.com/ansible/community/wiki/Galaxy

feedback:

• there's also a Galaxy working group wiki page, which is quite outdated. it would be nice to refresh it with some current info. for e.g. ansible-lint (now part of devtools) and Mazer can be removed, and galaxy_ng added. Another good example of a WG wiki page is the Network one.  https://github.com/ansible/community/wiki/Galaxy