Update-Guide.md

+Synchronize updates in this repository by pulling them from the remote:
+``` bash
+user@host:~/repo/blocks$ git pull
+```
+
+# Pulling from git when your local version has been modified
+Here's a typical scenario:
+``` console
+$ git checkout <branch>
+(git tells you it won't check out <branch> because you have changes you haven't committed)
+```
+
+You now have three choices:
+    1. Commit the changes to the current branch, because you know you want them
+    2. Delete the changes by reverting to the previous commit, because you know you don't want them
+    3. Store the changes locally, because you're not sure if you want them yet
+
+In case 1, you do:
+``` console
+$ git commit -am "<commit message>"
+$ git push
+```
+
+In case 2, you do:
+``` console
+$ git reset --hard HEAD
+```
+
+In case 3, you do:
+``` console
+$ git stash
+```
+
+After doing any of these three things you should be able to check out the branch you want without any issues.
+``` console
+$ git checkout <branch>
+```
+
+**BONUS:** Let's assume you were in case 3 and you stashed the changes, then checked out a working branch. Now you want to switch back to master and get back the changes you made. Here's what you do:
+``` console
+$ git checkout master
+$ git stash pop
+```
+
+For more information, see Git's official documentation for the stash command:
+https://git-scm.com/book/en/v1/Git-Tools-Stashing
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