Installation with asymmeteric algorithm support documentation

Author: vimalloc

docs/installation.rst

@@ -9,6 +9,20 @@ The easiest way to start working with this extension with pip:
 
   $ pip install flask-jwt-extended
 
+If you want to use asymmetric (public/private key) key signing algorithms, include
+the ``asymmetric_crypto`` extra requirements.
+
+.. code-block:: bash
+
+  $ pip install flask-jwt-extended[asymmetric_crypto]
+
+Note that if you are using ZSH (possibly other shells too), you will need to escape the brackets
+
+.. code-block:: bash
+
+  $ pip install flask-jwt-extended\[asymmetric_crypto\]
+
+
 If you prefer to install from source, you can clone this repo and run
 
 .. code-block:: bash