Update section-install.rst

installing-using-virtualenv has no instructions.

Removing the reference to it.

Author: dharmatech

source/guides/section-install.rst

@@ -6,7 +6,6 @@ Installation
    :titlesonly:
 
    installing-using-pip-and-virtual-environments
-   installing-using-virtualenv
    installing-stand-alone-command-line-tools
    installing-using-linux-tools
    installing-scientific-packages