Add custom logo config doc (#768)

* Add custom logo config doc

* Update ProActiveAdminGuide.adoc

src/docs/admin/ProActiveAdminGuide.adoc

@@ -969,6 +969,10 @@ The following important rules apply to global variables and generic information:
             </genericInformation>
 ----
 
+=== Custom logo configuration
+
+To be able to edit the default logo displayed in ProActive portals, you have to replace the following file `PROACTIVE_HOME/dist/war/getstarted/assets/image/custom-logo.png` with your custom logo.
+
 == User Authentication
 
 In order to use ProActive Scheduler every user must have an account. It supports three methods for authentication:
@@ -3472,4 +3476,4 @@ include::../CLI.adoc[]
 [[_cloud_infrastructure_startup_script]]
 === Cloud Node Source Infrastructure Startup Script
 include::./references/NodeSourceStartupScriptReference.adoc[]
-include::../common-footer.adoc[]
\ No newline at end of file
+include::../common-footer.adoc[]