Update Graylog.md (#15938)

I am using LibreNMS and graylog and it always bugged me that the api user have to be admin in graylog.
So i found out how you fix that :)

doc/Extensions/Graylog.md

@@ -67,10 +67,29 @@ can override the default of `/api/` using
     ```
 
 ## User Credentials
-If you choose to use another user besides the admin user, please note
-that currently you must give the user "admin" permissions from within
+If you don't want to use an admin account for connection to Graylog
+Log into http://<graylog-server-ip>/api/api-browser/global/index.html using graylog admin credentials
+Browse to: Roles: User roles
+Click on: Create a new role
+In JSON body paste this:
+
+```
+{
+	"name": "LibreNMS-Read",
+	"description": "Extended reading permissions for LibreNMS",
+	"permissions" : [
+		"searches:relative",
+		"streams:read"
+	]
+}
+```
+Press “Try it out”
+Log into graylog web ui as admin and add the role to the user
+
+Otherwise you must give the user "admin" permissions from within
 Graylog, "read" permissions alone are not sufficient.
 
+
 ## TLS Certificate
 If you have enabled TLS for the Graylog API and you are using a
 self-signed certificate, please make sure that the certificate is