docs(config): warn about federation key query timeout caveat

Signed-off-by: rooot <hey@rooot.gay>

conduwuit-example.toml

@@ -329,7 +329,8 @@
 # to high values, as dead homeservers can significantly slow down
 # federation, specifically key retrieval, which will take roughly the
 # amount of time you configure here given that a homeserver doesn't
-# respond.
+# respond. This will cause most clients to time out /keys/query, causing
+# E2EE and device verification to fail.
 #
 #federation_conn_timeout = 10
 

src/core/config/mod.rs

@@ -416,7 +416,8 @@ pub struct Config {
 	/// to high values, as dead homeservers can significantly slow down
 	/// federation, specifically key retrieval, which will take roughly the
 	/// amount of time you configure here given that a homeserver doesn't
-	/// respond.
+	/// respond. This will cause most clients to time out /keys/query, causing
+	/// E2EE and device verification to fail.
 	///
 	/// default: 10
 	#[serde(default = "default_federation_conn_timeout")]