Update docs to talk about libera.chat

[twisted-trac]

	@adiroiban reported
Trac ID	trac#10213
Type	enhancement
Created	2021-07-06 12:44:18Z

We no longer use freenode but https://web.libera.chat/

Searchable metadata

trac-id__10213 10213
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__1625575458233582 1625575458233582
changetime__1625588888643457 1625588888643457
version__None None
owner__Adi_Roiban__adiroiban_____ Adi Roiban <adiroiban@...>

[twisted-trac]

	@adiroiban commented

PR at #1611

[twisted-trac]

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

In changeset 61bda09

#!CommitTicketReference repository="" revision="61bda096c6813f3aaf75789992ec5c826c4d01c1"
Merge pull request #1611 from twisted/10213-libera-chat-docs

Author: adiroiban
Reviewer:  graingert
Fixes: ticket:10213

Remove freenode from the documentation/README and use Libera.chat.