Feat(docs): README: a note on Onionbalance usage

README.md

@@ -168,6 +168,19 @@ That means that passphrases should:
 * Either be destroyed along unused candidates OR, if stored, have the same
   storage security level than the .onion keypair.
 
+### Onionbalance compatibility
+
+When generating keys for [Onionbalance](https://onionbalance.readthedocs.io/en/latest/),
+make sure to use one pool per key:
+
+1. One pool for the frontend instance.
+2. One pool per backend instance.
+
+This is for security considerations: keys generated within the same pool are highly
+correlated. This means that if an attacker takes control of a backend instance that
+uses a keypair generated in the same pool, then the attacker can try to regenerate
+related keys.
+
 ## Tasks
 
 Check the [issue queue](https://gitlab.torproject.org/tpo/onion-services/onionmine/-/issues)