index: ML: link to subscribe and get info

From Lore, there is no explanation on how to subscribe.

Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>

index.md

@@ -150,7 +150,10 @@ for more details.
 
 ## Communication
 
-* Mailing List: [[email protected]](mailto:[email protected]) (and [archives](https://lore.kernel.org/mptcp))
+* Mailing List: [[email protected]](mailto:[email protected])
+  ([archives](https://lore.kernel.org/mptcp) -
+   [subscribe](mailto:[email protected]) -
+   [info](https://subspace.kernel.org/lists.linux.dev.html))
 * IRC: [#mptcp](https://web.libera.chat/?nick=mptcp-dev-guest?#mptcp) on libera.chat
 * Online [Meetings](https://github.com/multipath-tcp/mptcp_net-next/wiki/Meetings)
 * [Blog](https://blog.mptcp.dev)