licensing: add more instructions for updating license HTML file for a branch
licensing: add more instructions for updating license HTML file for a branch

Also fix a bug I introduced in CL:178129.

BUG=None
TEST=M33 licensing run

Change-Id: Ib8b898d17138f1d30692080b8e0eeb0bdd99ab07
Reviewed-on: https://chromium-review.googlesource.com/180875
Reviewed-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Commit-Queue: Yu-Ju Hong <52dc720c411f8e2156e608c1a8b894a917489667@chromium.org>
Tested-by: Yu-Ju Hong <52dc720c411f8e2156e608c1a8b894a917489667@chromium.org>

bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite