Missing documentation about desktop-focused software repos

[jonasrosland]

As discussed in Mattermost regarding the default software repos, when going into "Software", there aren't a lot of applications available. When going into the "Play" category for instance, it's blank.

Sokel mentioned enabling epel-release, and Skip mentioned adding Flathub as well.

If not shipped with these enabled by default, it should be documented how to easily enable these.

[sspencerwire]

@jonasrosland With the merge of PR #2030, I think that this issue can now be closed. I hope you agree! Normally, procedures that require the EPEL, include those instructions, so there should be no need for a separate resource for that one. Let me know, and "thank you!"

[sspencerwire]

@jonasrosland I'm going to close this for now. If you feel this is still an issue, please let us know!