Add docs to rename measurement

[thomaspeitz]

Me again :)

There was the docs missing to rename a measurement (which was the reason i found this project)

[oktal]

Thanks, did the rule work as expected ?

[thomaspeitz]

@oktal - Check worked. I did not apply. We decided to not make the migration in the end. The downtime for us was not worth it. We have 60GB of influx data and the downtime was not worth the renaming. We live with it.

[oktal]

Thanks for the feedback.

If you want minimum downtime, one solution would be to stop your node, copy your historical shard files in a temporary directory, start your node back, then run infix from your temp directory with -datadir.