Problem with exporting path of virtualenvwrapper.sh in install.rst

[yugant10ghimire]

Ubuntu 16.04 and onward the location of vritualenvwrapper’s pip installation changed from /usr/local/bin/virtualenvwrapper.sh to ~/.local/bin/virtualenvwrapper.sh.
This change should also be reflected in the documentation of installation.
thank you!

[naclonts]

Addressed in PR #71.