firefox: note that search engine policy is ESR-only

etc/firefox/policies/README.md

@@ -11,7 +11,9 @@ per whatever I am doing.
 <!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
 
 - [WARNING TO LIBREWOLF USERS](#warning-to-librewolf-users)
-- [Privacy Badger](#privacy-badger)
+- [Extensions](#extensions)
+  - [Privacy Badger](#privacy-badger)
+- [Search engines](#search-engines)
 - [See also](#see-also)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
@@ -25,7 +27,11 @@ This file takes priority over
 `/usr/share/librewolf/distribution/policies.json` so don't apply this or
 a lot of LibreWolf specific customizations stops being in force.
 
-## Privacy Badger
+## Extensions
+
+They are mostly self-explanatory.
+
+### Privacy Badger
 
 - `jid1-MnnxcxisBPnSXQ-eff@jetpack` - Downloaded directly from EFF.
 
@@ -37,6 +43,10 @@ See also:
 - https://github.com/EFForg/privacybadger/blob/master/doc/admin-deployment.md
 - https://github.com/EFForg/privacybadger/blob/master/src/data/schema.json
 
+## Search engines
+
+> Policy SearchEngines is only allowed on ESR
+
 ## See also
 
 - https://mozilla.github.io/policy-templates/