Add prefix for all commands in documentation (#2877)

* Add prefix for commands in docs

* Add prefix for commands in example's README

docs/patterns/appfactories.rst

@@ -91,14 +91,14 @@ Using Applications
 
 To run such an application, you can use the :command:`flask` command::
 
-    export FLASK_APP=myapp
-    flask run
+    $ export FLASK_APP=myapp
+    $ flask run
     
 Flask will automatically detect the factory (``create_app`` or ``make_app``) 
 in ``myapp``. You can also pass arguments to the factory like this::
 
-    export FLASK_APP="myapp:create_app('dev')"
-    flask run
+    $ export FLASK_APP="myapp:create_app('dev')"
+    $ flask run
     
 Then the ``create_app`` factory in ``myapp`` is called with the string
 ``'dev'`` as the argument. See :doc:`/cli` for more detail.

docs/patterns/packages.rst

@@ -61,19 +61,19 @@ a big problem, just add a new file called :file:`setup.py` next to the inner
 In order to run the application you need to export an environment variable
 that tells Flask where to find the application instance::
 
-    export FLASK_APP=yourapplication
+    $ export FLASK_APP=yourapplication
 
 If you are outside of the project directory make sure to provide the exact
 path to your application directory. Similarly you can turn on the
 development features like this::
 
-    export FLASK_ENV=development
+    $ export FLASK_ENV=development
 
 In order to install and run the application you need to issue the following
 commands::
 
-    pip install -e .
-    flask run
+    $ pip install -e .
+    $ flask run
 
 What did we gain from this?  Now we can restructure the application a bit
 into multiple modules.  The only thing you have to remember is the