README: Add Discord invite link

Add invite link to Discord per announcement email at
https://lore.kernel.org/openbmc/20201112145740.GB4495@heinlein/
Added in the openbmc/openbmc README at
https://gerrit.openbmc-project.xyz/c/openbmc/openbmc/+/38195

Change-Id: I8029d24f46cf3f59016e154c51384e70ab9b5bda
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/README.md b/README.md
index d1d3d82..312ce66 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,7 @@
 ## Contact
 
 - Mail: openbmc@lists.ozlabs.org [https://lists.ozlabs.org/listinfo/openbmc](https://lists.ozlabs.org/listinfo/openbmc)
+- Discord: https://discord.gg/69Km47zH98
 - IRC: #openbmc on freenode.net
 
 ## OpenBMC Development