fix(env.template): IP_HEADER defaults to X-Real-IP

This was wrong in commit 88c56de97b.

.env.template

@@ -36,9 +36,9 @@
 ## Automatically reload the templates for every request, slow, use only for development
 # RELOAD_TEMPLATES=false
 
-## Client IP Header, used to identify the IP of the client, defaults to "X-Client-IP"
+## Client IP Header, used to identify the IP of the client, defaults to "X-Real-IP"
 ## Set to the string "none" (without quotes), to disable any headers and just use the remote IP
-# IP_HEADER=X-Client-IP
+# IP_HEADER=X-Real-IP
 
 ## Cache time-to-live for successfully obtained icons, in seconds (0 is "forever")
 # ICON_CACHE_TTL=2592000