[#49] Merging guidelines: explain how to merge 'out of sync' branches (#63)
[#49] Merging guidelines: explain how to merge 'out of sync' branches (#63)

Instructions for merging out-of-sync branches require
merging master branch to PR branch using GitHub interface.

Recent changes to the workflow requires rebasing instead of
merging. However, out-of-sync branches can be merged if
CI can pass again based on the latest master branch.

Lets' update merging instructions to incorporate the above
changes.
oss-generic/process