When changes are merged to both hexops/mach and hexops/mach-glfw, we get a conflict
which is difficult to resolve with `git subtree`, particularly because we don't want
to squash commits for either repository (we prefer to maintain the full commit history
in both repos.)
Instead, require that all pull requests be sent to the main hexops/mach repository.
That's not as nice, I admit, but should be pretty easy to handle (literally just copy
changes over) and will ensure we can always keep both repos in sync easily and without
conflict.
Signed-off-by: Stephen Gutekanst <stephen@hexops.com>
