Documentation/community: Add link to the OSF Slack

We are also present on Slack so advertise that.

Change-Id: I7d9887e524e47e6f42a5013e9f696881ef54a631
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55036
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/Documentation/community/forums.md b/Documentation/community/forums.md
index c6c913e..2ad69e1 100644
--- a/Documentation/community/forums.md
+++ b/Documentation/community/forums.md
@@ -15,7 +15,9 @@
 
 We also have a real time chat room on [IRC](ircs://irc.libera.chat/#coreboot),
 also bridged to [Matrix](https://matrix.to/#/#coreboot:libera.chat) and a
-[Discord](https://discord.gg/JqT8NM5Zbg) presence.
+[Discord](https://discord.gg/JqT8NM5Zbg) presence. You can also find us on
+[OSF Slack](https://osfw.slack.com/), which has channels on many open source
+firmware related topics.
 
 ## Fortnightly coreboot leadership meeting