Update headless.mdx

Author: towneh

content/docs/server/headless.mdx

@@ -213,3 +213,5 @@ If the headless clients do not connect, check these first:
 - The client and server versions are compatible
 
 If you are scaling many instances and seeing instability, reduce the instance count and confirm whether the limit is memory, CPU, network bandwidth, or the server's configured `PeerLimit`.
+
+It is also advisable to have a considerable amount of virtual memory available for Unity in order to run without experiencing 137 exit codes (Out of Memory) in Docker.