Fix minor things in README

Correct nested lists, capitalize browser names and languages consistently, link to more information consistently
Merge pull request #1332 from tobiasvl/minor-readme-fixes

Fix minor things in README

thanks, housekeeping is always appreciated!
return dummy notification object if notification cannot be shown
np "don't vote" batched

"undo" button don't show the notification more than once every five seconds
"undo" button unvotes every vote you've made on this pageload
batch "np-don't vote" notification/button action

"undo" notification fires at most once every five seconds
"undo" button undoes all votes from this pageload

could use a little polish but whatever