Add documentation showing how to share configuration

[rnc]

Please DO NOT FORCE PUSH. Don't worry about messy history, it's easier to do code review if we can tell what happened after the review, and force pushing breaks that.

Please make sure that your PR allows edits from maintainers. Sometimes it's faster for us to just fix something than it is to describe how to fix it.

After creating the PR, please add a commit that adds a bullet-point under the [Unreleased] section of CHANGES.md, plugin-gradle/CHANGES.md, and plugin-maven/CHANGES.md which includes:

• a summary of the change
• either
  • a link to the issue you are resolving (for small changes)
  • a link to the PR you just created (for big changes likely to have discussion)

If your change only affects a build plugin, and not the lib, then you only need to update the plugin-foo/CHANGES.md for that plugin.

If your change affects lib in an end-user-visible way (fixing a bug, updating a version) then you need to update CHANGES.md for both the lib and all build plugins. Users of a build plugin shouldn't have to refer to lib to see changes that affect them.

This makes it easier for the maintainers to quickly release your changes :)

Fixes #2428

[rnc]

@nedtwigg Can this be reviewed please? :-)

[nedtwigg]

This will get merged eventually, but I have enough edits that it's easier to just edit it than request changes.

If there is some other task blocked on this let me know, otherwise I will probably not get around to this until enough PRs get merged to warrant a release.

[rnc]

@nedtwigg Thanks for the reply. I have nothing blocked on this ; this was the bit I found was missing from the docs in order not to have store the format styles locally in each repository. I'd be happy to edit if you wish.