Add documentation for how to check out beta

[amccreight]

I'm sure this just demonstrates that I have no idea how cinnabar actually works, but I am unable to figure out (based on "Mozilla: A git workflow for Gecko development" and the README.md) how to check out mozilla-beta locally. I'm trying to rebase a patch for beta. I have mozilla-unified as my remote, and that contains a59d9203232d, but running hg2git on that returns 0000000000000000000000000000000000000000 so there must be something else I need to do.

[mykmelez]

It works for me after cloning mozilla-unified from scratch using git-cinnabar:

> git clone hg::https://hg.mozilla.org/mozilla-unified
Cloning into 'mozilla-unified'...
Getting clone bundle from https://hg.cdn.mozilla.net/mozilla-unified/12214b5efbe48a6e6ccb44ce33e9d4ffb591bb28.zstd-max.hg
Reading 441885 changesets
Reading 440980 manifests
Reading and importing 2495422 files
Importing 440980 manifests
Importing 441885 changesets
Reading 116 changesets
Reading 116 manifests
Reading and importing 344 files
Importing 116 manifests
Importing 116 changesets

Run the following command to update tags:
  git fetch --tags hg::tags: tag "*"
> cd mozilla-unified/
> git cinnabar hg2git a59d9203232d
eff6f3d0a9a88274673d18217568761d6cd598f5

If you cloned mozilla-unified without using git-cinnabar, then the issue is probably that you don't have the metadata that git-cinnabar needs to translate Mercurial IDs to Git IDs (and vice-versa). In that case, you should be able to fix that by adding the repo as a remote and then fetching it:

git remote add unified hg::https://hg.mozilla.org/mozilla-unified
git fetch unified

[amccreight]

No, I used git-cinnabar. I ran the git fetch command you put there and now it works, so maybe I was missing that. I had a "tags" repo that I added following directions from somewhere on the docs but I guess I didn't do enough.

[annygakh]

Hi, Is this still in need of docs? I, too, struggled with this when trying to checkout beta and esr*, so I wrote down some notes for myself and I would be happy to write something up.

[glandium]

There is nothing about beta or esr on https://github.com/glandium/git-cinnabar/wiki/Mozilla:-A-git-workflow-for-Gecko-development but it shouldn't be much different from how you interact with central. Adding a section about non-central branches would probably be a good thing. Please feel free to do so.