Clarify README.HACKING

[tom]

As an alternative, if you have your patch in a git repository, you can
edit projects/firefox/config to change the git_url option to point to
your git repository, and change the git_hash option to point to the
commit you want to build. You will also need to comment the
'tag_gpg_id: 1' line (unless git_hash is pointing to a signed git tag).

I presume the current value of git_hash is a tag (and not a branch) right? It'd be good to explain that.

Even better would be if we could build off branches. I guess my ideal situaiton would be:

As an alternative, if you have your patch in a git repository, you can
edit projects/firefox/config to change the git_url option to point to
your git repository.

You can specify git_hash to build off a commit hash or tag, OR
git_branch to build off a branch. (If both are specified, it is an
error.) git_branch may be 'remotename/branchname' in which case the
remote branch is git fetch-ed and then built; or 'branchname' in
which case the local branch is git checkout-ed and then built.

[boklm]

The value of git_hash has to be a tag if tag_gpg_id is set to 1. Otherwise it can be anything that is understood by git, including a branch. If you specify a branch, you don't need to specify a remotename, as all branches from the git_url are created as local branches (with git fetch origin +refs/heads/*:refs/heads/*). So it is not a good idea to create local branches in git_clones/* as they can be removed if the remote repository has a branch with the same name. If you want to use local branches, it is better to create them in a separate repository, and change git_url to file:///path to point to your repository.

[boklm]

The branch bug_23630 has a patch that should clarify the README.HACKING file:
​https://gitweb.torproject.org/user/boklm/tor-browser-build.git/commit/?h=bug_23630&id=dd09e0d57edc1017c5f2b158b0b19e8ab25220d9

[gk]

Thanks, looks good and applied to master (commit 43e5d8803933af80e6e71005a5f64338c91680d7).