Add release strategy to community documentation

[zklaus]

This adds the release strategy as discussed in the core team.

Please feel free to make further comments and suggestions before we fully commit to this strategy by merging it into master!

@nielsdrost, could you please let me know when you are done with the figure or just add it to this PR?

NB: If adopted, the next feature freeze is scheduled for 2020-10-05 and the next release will be overseen by @valeriupredoi, so I propose to merge this within the next two weeks if possible.

[zklaus]

I added the people that were in the video call or had expressed interest in it as well as the PIs as reviewers.

However, in the spirit of an open community, everyone is welcome to comment.

[bouweandela]

Thanks @zklaus! @ESMValGroup/esmvaltool-developmentteam Any comments?

[nielsdrost]

@nielsdrost, could you please let me know when you are done with the figure or just add it to this PR?
I added the figure to this branch. It's a diagrams.net (formally draw.io) image, with the vector image embedded in the png (holy backward metadata batman!)

[axel-lauer]

First of all, nice work! I particularly like the definition of the terms in the glossary. Two comments on the current version:

(1) I think since this document will be part of the user's guide, the wording should be a bit more "determined". E.g. instead of "The goal of this document is to lay out [...]" simply "This document lays out [...]" or instead of "We propose to follow a strategy of timed releases." simply "We aim at following a strategy of timed releases.".

(2) I am still a bit worried that such frequent releases might be to much. Too much in terms of additional work and possibly also confusing for scientist users as there are new versions of the tool "all the time". But I am fine trying to follow the proposed release schedule and see how it goes.

[nielsdrost]

First of all, nice work! I particularly like the definition of the terms in the glossary. Two comments on the current version:

(1) I think since this document will be part of the user's guide, the wording should be a bit more "determined". E.g. instead of "The goal of this document is to lay out [...]" simply "This document lays out [...]" or instead of "We propose to follow a strategy of timed releases." simply "We aim at following a strategy of timed releases.".

I second that comment, and added some text suggestions to "implement" this.

[zklaus]

Thanks @axel-lauer for the suggestions and @nielsdrost for the figure and implementing the suggestion by Axel. I commited them.

[bouweandela]

Thanks, I hope this will increase transparency.