doc: doc/README.md IRC updates

- update remaining link and reference from freenode to libera
- remove no-longer-existing #bitcoin-dev IRC channel
- other minor fixups

Author: jonatack

doc/README.md

@@ -30,8 +30,8 @@ Drag Bitcoin Core to your applications folder, and then run Bitcoin Core.
 
 * See the documentation at the [Bitcoin Wiki](https://en.bitcoin.it/wiki/Main_Page)
 for help and more information.
-* Ask for help on the [Bitcoin StackExchange](https://bitcoin.stackexchange.com)
-* Ask for help on [#bitcoin](https://webchat.freenode.net/#bitcoin) on Freenode. If you don't have an IRC client, use [webchat here](https://webchat.freenode.net/#bitcoin).
+* Ask for help on [Bitcoin StackExchange](https://bitcoin.stackexchange.com).
+* Ask for help on #bitcoin on Libera Chat. If you don't have an IRC client, you can use [web.libera.chat](https://web.libera.chat/#bitcoin).
 * Ask for help on the [BitcoinTalk](https://bitcointalk.org/) forums, in the [Technical Support board](https://bitcointalk.org/index.php?board=4.0).
 
 Building
@@ -68,8 +68,7 @@ The Bitcoin repo's [root README](/README.md) contains relevant information on th
 
 ### Resources
 * Discuss on the [BitcoinTalk](https://bitcointalk.org/) forums, in the [Development & Technical Discussion board](https://bitcointalk.org/index.php?board=6.0).
-* Discuss project-specific development on #bitcoin-core-dev on Libera Chat. If you don't have an IRC client, use [webchat here](https://web.libera.chat/#bitcoin-core-dev).
-* Discuss general Bitcoin development on #bitcoin-dev on Freenode. If you don't have an IRC client, use [webchat here](https://webchat.freenode.net/#bitcoin-dev).
+* Discuss project-specific development on #bitcoin-core-dev on Libera Chat. If you don't have an IRC client, you can use [web.libera.chat](https://web.libera.chat/#bitcoin-core-dev).
 
 ### Miscellaneous
 - [Assets Attribution](assets-attribution.md)