IRC => Slack in docs

[mi-wood]

We should update the docs to have people request slack invites, since we don't user IRC anymore

[DeeDeeG]

A search of the repo's code turns up two mentions of IRC:

• travis.yml
  • README.md The Travis config file apparently notifies the IRC channel of Travis' activities. Not sure if want to get rid of that or not. (I've never personally been on the IRC channel so I have no investment there either way.)

Readme.md just says

## IRC

Server: irc.freenode.com
Channel: #refugerestrooms

---

Could probably be replaced with

## Slack

Request an invite to RefugeLGBT's Slack page here: [#286](https://github.com/RefugeRestrooms/refugerestrooms/issues/286)

Or...

## Slack

Email Teagan for an invite to our Slack: [email@example.com](mailto:email@example.com)

Or... etc.

I'm not sure who they should contact, or if they should open a new issue, etc. but it seems like it would entail a simple update to the readme.

[DeeDeeG]

For what it's worth, I looked into just linking people to refugelgbt.slack.com, thinking there would be a "request invite" link, but there isn't one. It simply says to contact the administrators: