Clarify docs on Redis package required for caching (#2557)

docs/installation.rst

@@ -240,9 +240,11 @@ complies with the Flask-Cache specifications.
 
 Flask-Cache supports multiple caching backends (Redis, Memcached,
 SimpleCache (in-memory), or the local filesystem). If you are going to use
-Memcached please use the pylibmc client library as python-memcached does
+Memcached please use the `pylibmc` client library as `python-memcached` does
 not handle storing binary data correctly. If you use Redis, please install
-`python-redis <https://pypi.python.org/pypi/redis>`.
+the `redis <https://pypi.python.org/pypi/redis>`_ Python package: ::
+
+    pip install redis
 
 For setting your timeouts, this is done in the Superset metadata and goes
 up the "timeout searchpath", from your slice configuration, to your