Update layout_bootstrap3 readme paths

The paths in this readme were no longer correct.

examples/layout_bootstrap3/README.rst

@@ -14,11 +14,11 @@ To run this example:
 
 3. Install requirements::
 
-    pip install -r 'examples/layout-bootstrap3/requirements.txt'
+    pip install -r 'examples/layout_bootstrap3/requirements.txt'
 
 4. Run the application::
 
-    python examples/layout-bootstrap3/app.py
+    python examples/layout_bootstrap3/app.py
 
 The first time you run this example, a sample sqlite database gets populated automatically. To suppress this behaviour,
 comment the following lines in app.py:::