Add gitter chat tab to documentation

[twisted-trac]

	@adiroiban reported
Trac ID	trac#10245
Type	enhancement
Created	2021-08-01 12:33:06Z

To get something like the "Open Chat" bottom right tab from www.starlette.io

use https://sidecar.gitter.im/

we might need to copy the JS file and host it as a static file.

And add a custom JS.

https://docs.readthedocs.io/en/stable/guides/adding-custom-css.html

Searchable metadata

trac-id__10245 10245
type__enhancement enhancement
reporter__adiroiban adiroiban
priority__normal normal
milestone__None None
branch__ 
branch_author__ 
status__closed closed
resolution__fixed fixed
component__core core
keywords__review review
time__1627821186723545 1627821186723545
changetime__1627841716694678 1627841716694678
version__None None
owner__Adi_Roiban__adiroiban_____ Adi Roiban <adiroiban@...>

[twisted-trac]

	@adiroiban commented

PR at #1649

[twisted-trac]

	@adiroiban set owner to @adiroiban @adiroiban set status to closed

In changeset 34f3d8f

#!CommitTicketReference repository="" revision="34f3d8f8c6f51772eaed92a89257ea011e9a818d"
Merge pull request #1649 from twisted/10245-gitter-docs-integartion

Author: adiroiban
Reviewer: graingert 
Fixes: ticket:10245

Add Gitter sidecar chat button to documentation pages.