Removed vagrant-shell-scripts folder

This folder should not have been committed into this repository as we
are trying to use it as a submodule.
Re-Added Submodule vagrant-shell-scripts
Updated README.md

Resolving the issue of unmatched VirtualBox Guest Additions requires
the installation of vagrant-vbguest plugin prior to setup and no
further changes to configuration. Hence, the README.md is updated with
a small section with regards to vagrant-vbguest.

Minor changes to the README.md was also made to enhance the
instructions.
Merge pull request #4 from prixde/Enhancement/Issue3/Non-Matching-Virtualbox-Guest-Additions

Updated README.md
Merge pull request #2 from prixde/Bug/Issue1/Submodule-Not-Properly-Set-Up

Bug/issue1/submodule not properly set up