Add link to chrome and firefox addon store in README.md

[djmgit]

Add links to chrome and firefox addon store in README.md

What you actually need to do

chrome app store link: https://chrome.google.com/webstore/detail/fearch/kalmlbhhgndofalfencmggfncedfajgj?hl=en Firefox AMO link https://addons.mozilla.org/en-US/firefox/addon/fearchit/?src=userprofile

You have to insert the above mentioned links in README.md file.