Trunk readme workflow needs improvement

[boonebgorges]

• When building a new branch, fix the readme so that it says something coherent
• When creating a tag, ensure that the proper readme is not overwritten
• When bumping trunk stable tag, grab the whole readme (? but this will break Development strings in GlotPress), or at least the Changelog and Upgrade Notice sections

[boonebgorges]

Also, make sure that Requires at least version is not changed in minor releases