Add prefix for all commands in documentation (#2877)

* Add prefix for commands in docs

* Add prefix for commands in example's README

docs/tutorial/deploy.rst

@@ -21,7 +21,7 @@ is installed first:
 
 .. code-block:: none
 
-    pip install wheel
+    $ pip install wheel
 
 Running ``setup.py`` with Python gives you a command line tool to issue
 build-related commands. The ``bdist_wheel`` command will build a wheel
@@ -29,7 +29,7 @@ distribution file.
 
 .. code-block:: none
 
-    python setup.py bdist_wheel
+    $ python setup.py bdist_wheel
 
 You can find the file in ``dist/flaskr-1.0.0-py3-none-any.whl``. The
 file name is the name of the project, the version, and some tags about
@@ -41,7 +41,7 @@ file with ``pip``.
 
 .. code-block:: none
 
-    pip install flaskr-1.0.0-py3-none-any.whl
+    $ pip install flaskr-1.0.0-py3-none-any.whl
 
 Pip will install your project along with its dependencies.
 
@@ -50,8 +50,8 @@ create the database in the instance folder.
 
 .. code-block:: none
 
-    export FLASK_APP=flaskr
-    flask init-db
+    $ export FLASK_APP=flaskr
+    $ flask init-db
 
 When Flask detects that it's installed (not in editable mode), it uses
 a different directory for the instance folder. You can find it at
@@ -70,7 +70,7 @@ You can use the following command to output a random secret key:
 
 .. code-block:: none
 
-    python -c 'import os; print(os.urandom(16))'
+    $ python -c 'import os; print(os.urandom(16))'
 
     b'_5#y2L"F4Q8z\n\xec]/'
 
@@ -99,7 +99,7 @@ first install it in the virtual environment:
 
 .. code-block:: none
 
-    pip install waitress
+    $ pip install waitress
 
 You need to tell Waitress about your application, but it doesn't use
 ``FLASK_APP`` like ``flask run`` does. You need to tell it to import and
@@ -107,7 +107,7 @@ call the application factory to get an application object.
 
 .. code-block:: none
 
-    waitress-serve --call 'flaskr:create_app'
+    $ waitress-serve --call 'flaskr:create_app'
 
     Serving on http://0.0.0.0:8080