New answer
You seem to be looking for git-cherry-pick . This command is used to capture a named commit and pass it to the current branch. The main syntax is git cherry-pick <commit> ; here is the man page .
However, you should avoid picking cherries whenever possible, as it creates repeated fixations, and you really want to see them as merges. You should try to accept a branch workflow that merges up. From man gitworkflows :
Always commit your fixes to the oldest supported branch that requires them. Then (periodically) merge the integration branches up to each other.
This gives a very controlled stream of fixes. If you notice that you applied the fix, for example. the master, which is also required in maint, you will need to select it (using git -cherry-pick (1)) down. This will happen several times, and you have nothing to worry about if you do not do it very often.
In your case, you can split documentation updates into several classes, for example. "featureA-documentation", each of which will be merged into one or more branches. You can easily write yourself a script to automate checking various branches and merging into relevant topics.
Old Answers
Look at the history of changes, if you are interested - they considered how to get corrections from several branches from a local repo to a remote one, with the publication of push or patch.