Doc how to pip install a given commit

doc/install.txt

@@ -308,6 +308,18 @@ to your ``Theano`` folder and execute the following command:
 You should update frequently, bugs are fixed on a very regular basis.
 
 
+Specific git commit
+~~~~~~~~~~~~~~~~~~~
+
+You can install a specific git commit by using the bleeding edge
+instruction and adding @COMMIT_ID to the pip command like:
+
+.. code-block:: bash
+
+    pip install --upgrade --no-deps git+git://github.com/Theano/Theano.git@07e9332a0932e90c47ed2a70fc3c7f8a55d2aa23
+
+
+
 .. _testing_installation:
 
 Testing your installation