Adapt the README.HACKING document to allow the user to modify the correct git_hash when testing branches/commits
I tried to test the patches for #16778 (moved) and did the following in my tor-browser-build
repo
-git_hash: 'tor-browser-[% c("var/firefox_version") %]-[% c("var/torbrowser_branch") %]-1-build2'
-tag_gpg_id: 1
-git_url: https://git.torproject.org/tor-browser.git
+git_hash: 'bug16778_v2'
+tag_gpg_id: 0
+git_url: https://github.com/sysrqb/tor-browser
After doing a |make fetch| and |make testbuild| the new commits are not used. I verified that by inspecting the .tar ball we use in our container for building.