Bug 490112 - Add unique id to p2 user agent information

Add a comment explaining how to disable UUID 
Change-Id: I54f6eb166a05ce377a5048c09b11f35847b18175
Signed-off-by: Pascal Rapicault <pascal@rapicorp.com>
diff --git a/bundles/org.eclipse.core.runtime/src/org/eclipse/core/internal/runtime/InternalPlatform.java b/bundles/org.eclipse.core.runtime/src/org/eclipse/core/internal/runtime/InternalPlatform.java
index 728f4eb..09c044f 100644
--- a/bundles/org.eclipse.core.runtime/src/org/eclipse/core/internal/runtime/InternalPlatform.java
+++ b/bundles/org.eclipse.core.runtime/src/org/eclipse/core/internal/runtime/InternalPlatform.java
@@ -751,7 +751,8 @@
 			Properties prop = new Properties();
 			prop.setProperty(PROP_UUID, uuid);
 			prop.setProperty("version", "1"); //$NON-NLS-1$//$NON-NLS-2$
-			prop.store(os, ""); //$NON-NLS-1$
+			prop.store(os,
+					"To opt-out from using a UUID for all your eclipse instances, please change this value to 0. If you only want to opt-out for one instance, then add eclipse.uuid=0 in the config.ini. If you delete this file, a new UUID will be created"); //$NON-NLS-1$
 		} catch (IOException e) {
 			return;
 		}