Updated SECRET_KEY instructions for HA installs. Issue 295

docs/installation/netbox.md

@@ -110,6 +110,8 @@ DATABASE = {
 
 Generate a random secret key of at least 50 alphanumeric characters. This key must be unique to this installation and must not be shared outside the local system.
 
+In the case of a highly available installation with multiple web servers, SECRET_KEY must be identical between all server in order to maintain a persistent user session state between servers.
+
 You may use the script located at `netbox/generate_secret_key.py` to generate a suitable key.
 
 # Run Database Migrations