We are a team of 60+ developers working on the same product and are moving from SVN to Git and GitHub. We have a process in SVN where in individual files are locked and when
If you are using git LFS (which is supported by some git hosting providers, like GitHub) you could use File Locking.
Mark a file type as lockable by editing the .gitattributes file:
*.docx lockable
# Make MS Word files lockable
And lock it with:
$ git lfs lock example.docx
You can unlock your files with git lfs unlock example.docx and those of somebody else by adding --force.