Update README.md

Here are the finalized changes:

* Made typo and grammar corrections.
* Clarified user ID issue as it pertains to 8chan.
* Changed all short URLs back to target (long) URLs, except for git.io URLs.
* Removed https:// from archive.today, saving us one link. Added .com to donotlink, but no http://, so its non-link status is unchanged.
* Added link to "Twitter Flooding Instructions.md" after "Be civil if you have to argue with people on Twitter"
* Added link to "shills.md" after "Ignore derailers and shills".
* Added "Boycott list ..." link to a repo I'm maintaining.
* Added #GamerGate Community link to "Other discussion locations"
* Added explanation (outside of copypasta) that 4chan's 2000 character limit is no longer in effect.
* This results in 23 links, so I hxxp'ed the article links, getting us down to 20 links. I contacted Based Hotwheels to increase the link limit. If and when he does, we can revert them to http.
* Final count is 20 links, 2415 characters.