Added note about checking for merged branches

This should check if your commits are fully merged or not. Mostly taken from
http://stackoverflow.com/questions/7548926/git-and-the-branch-x-is-not-fully-merged-error.

README.md

@@ -52,6 +52,7 @@ For clarity's sake all examples in this document use a customized bash prompt in
     - [Delete/remove arbitrary commit](#deleteremove-arbitrary-commit)
     - [Delete tag](#delete-tag)
   - [Deleted Patch](#deleted-patch)
+  - [Check if all commits on a branch are merged](#check-if-all-commits-on-a-branch-are-merged)
 - [Other Resources](#other-resources)
   - [Books](#books)
   - [Tutorials](#tutorials)
@@ -650,6 +651,21 @@ If someone has sent you a pull request on GitHub, but then deleted their origina
 
 After commiting, change the author of the previous commit. To do this, see how to [change author](#commit-wrong-author). Then, apply whatever changes needed on to, and make a new pull request.
 
+<a name="check-if-all-commits-on-a-branch-are-merged"></a>
+## Check if all commits on a branch are merged
+
+To check if all commits on a branch are merged into another branch, you should diff between the heads (or any commits) of those branches:
+
+```sh
+(master)$ git log --graph --left-right --cherry-pick --oneline HEAD...feature/120-on-scroll
+```
+
+This will tell you if any commits are in one but not the other, and will give you a list of any nonshared between the branches. Another option is to do this:
+
+```sh
+(master)$ git log master ^feature/120-on-scroll --no-merges
+```
+
 # Other Resources
 
 ## Books