Minor docs update.

docs/source/installing.rst

@@ -9,6 +9,9 @@ Dependencies
   - six
   - nbformat
 
+Note the requirement 2.7.1, not 2.7.0, this is because
+2.7.1 fixes a bug in difflib in an interface-breaking way.
+
 Dependencies for running tests:
 
   - pytest
@@ -19,17 +22,17 @@ Install
 -------
 Use pip to install. See the pip documentation for options. Some examples:
 
-Global install
+Install requirements for the current user only:
 
-    pip install .
+    pip install --user --upgrade -r requirements.txt
 
-Local install
+Install nbdime for the current user only:
 
-    pip install --user .
+    pip install --user --upgrade .
 
-Local developer install
+Make a local developer install for the current user only:
 
-    pip install -e --user .
+    pip install --user --upgrade -e .
 
 
 Testing
@@ -44,7 +47,12 @@ To run tests, locally, simply run
 
     py.test
 
-from the project root. See the pytest documentation for more options.
+from the project root. If you have python 2 and python 3 installed,
+you may need to run
+
+    python3 -m pytest
+
+to run the tests with python 3. See the pytest documentation for more options.
 
 If you have notebooks with interesting merge challenges,
 please consider contributing them to nbdime as test cases!