meta: update the link to the ML

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

We started using the delvingbitcoin bitcoin until we decided to switch to another platform last year. See [1] for more details

[1. ML Future discussion](https://lists.linuxfoundation.org/pipermail/lightning-dev/2023-December/004231.html)
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)