Update Commit example documentation to mention index.write after committing

[nanodeath]

The documentation mentions, in one place, at least, how to commit a newly written index (using index.write_tree(repo)), but fails to mention that index.write should be called after the commit has been performed. This is a bit unintuitive to me, so it'd be nice if the API could be improved, but barring that, at least add that one line to the documentation (index.write).

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This issue seems somewhat common -- it's come up at least twice: on GitHub as well as on StackOverflow. On the SO question, Carlos does say That example does not emulate the git-commit command, it just creates a new commit., but since some people (at least me and two others) expect it to work this way, it seems like it'd be worth calling out, at least.

[arthurschreiber]

Ok, thanks for reporting this. I'll add this to the documentation as soon as I can find some free time.

[carlosmn]

Noe that adding persisting the repository object is not going to make it look any more like git-commit, it will just be different in a different way. No git-commit invocation overwrites the contents of a file for the commit.