It's quite common to open up a pull request on GitHub and be confronted with the message This branch has conflicts that must be resolved. This situation arises when you create a feature branch on an older commit from the master branch. Maybe you forgot to run git pull master before git checkout -b geocoding_vignette or maybe a collaborator changed some of the same files on GitHub while you've been working on new things. There are many ways to fix this. One is using the Web Editor build into GitHub and fixing conflicts by hand. This works great if there are not too many conflicts.
Another technique is to rebase your pull request onto the master branch (Move your additional commits on top of the most recent master commit). This is conceptually clean, but sometimes confusing in practice to do cleanly. This example walks through the process where you want to do a rebase, and resolve conflicts by overwriting whatever is on the master branch with change