Add snap install instructions
Add snap install instructions

Thanks for publishing Slashlock in the snap store!

This pull request adds installation instructions for users of [snap enabled Linux distributions](https://snapcraft.io/docs/core/install). Snaps enable ISVs and projects to make their software available to millions of Linux users via the snap store and directly control delivery of software updates to their users. Snaps of stable desktop applications will also be available via the desktop Software Center, improving the discoverability of your software. Your software can be installed with a simple `snap install shashlock` simplifying the installation instructions for your users.
wookalar/slashlockgui,wookalar/slashlockgui