Update CONTRIBUTING with remote change instructions (#2)

CONTRIBUTING.md

 If you want to contribute to Theano, have a look at the instructions here:
 http://deeplearning.net/software/theano/dev_start_guide.html
+
+
+## Migrating PRs from original Theano Repo
+Theano-PyMC is actively merging new changes. If you have a pull request on the original respository and would like to move it here use the following commands in your local theano repo
+
+```
+# Go to your Theano Repo
+cd /path/to/your/repo
+
+# If you'd like to add theano-PyMC as a remote
+git remote add pymc git@github.com:pymc-devs/Theano-PyMC.git
+
+# Verify the changes. You should see the pymc-devs/Theano-PyMC.git
+git remote -v
+
+# Checkout the branch of your request
+git checkout branch_name
+
+# Push to Theano-PyMC
+git push pymc branch_name
+```
+
+If you'd like to completely run this command instead
+
+```
+# If you'd like to replace this repo as a remote
+git remote set-url origin git@github.com:pymc-devs/Theano-PyMC.git
+```