Fixing "Fore" -> "For" typo in README docs. (#4317)

Also obeying an 80-column limit for the content and
adding a missing "``virtualenv``" in the phrase
"``pip`` and ``virtualenv``" in some of the docs.

Author: dhermes

packages/google-cloud-vision/README.rst

@@ -18,7 +18,9 @@ Quick Start
 
     $ pip install --upgrade google-cloud-vision
 
-Fore more information on setting up your Python development environment, such as installing ``pip`` on your system, please refer to `Python Development Environment Setup Guide`_ for Google Cloud Platform.
+For more information on setting up your Python development environment,
+such as installing ``pip`` and ``virtualenv`` on your system, please refer
+to `Python Development Environment Setup Guide`_ for Google Cloud Platform.
 
 .. _Python Development Environment Setup Guide: https://cloud.google.com/python/setup