meta: update the link to the ML

This commit is updating the link to the ML and
redirect user to delvingbitcoin forum.

We start using the delvingbitcoin bitcoin till last year
we decided to switch to another platform. See
[1](https://lists.linuxfoundation.org/pipermail/lightning-dev/2023-December/004231.html)
for more details

Signed-off-by: Vincenzo Palazzo <[email protected]>

Author: vincenzopalazzo

README.md

@@ -5,7 +5,7 @@ drafted.
 
 Pull requests and comments welcome, seeking input from community stakeholders.
 
-Discussion available on the [lightning-dev mailing list](https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev).
+Discussion available on the [delvingbitcoin](https://delvingbitcoin.org/tag/lightning).
 
 ### [Start here for Table of Contents](00-introduction.md)