Issue 7202 - Point development guide to contributing section

[mcsitter]

• Create a new changelog file
• Tox docs environment passed successfully

Resolves #7202

As proposed the development guide now points to the contributing section.

Instead of embedding RELEASING.rst a link to GitHub is now present. Since only a few people who contribute need to now the release procedure this solution seems appropriate. Adding a new releasing section to the documentation would provoke the same maintenance issues the development guide has now to occur on the releasing section.

I also allowed myself to add a note about the maintenance of the development guide.

Open for feedback!

[bluetech]

Thanks for doing this @mcsitter! I left a couple of comments, will merge after they are fixed.

[webknjaz]

Why was the mention of the label management removed? @nicoddemus do you know? Is the automation still in use?

cc @RonnyPfannschmidt

[nicoddemus]

TBH I completely forgot about that, and suspect we have never used it really, so that labels.toml file has not been used in awhile.