ffi-crypto-bindings: Improve comments

bindings/matrix-sdk-crypto-ffi/src/machine.rs

@@ -1537,6 +1537,11 @@ impl OlmMachine {
 
     /// Clear any in-memory caches because they may be out of sync with the
     /// underlying data store.
+    /// 
+    /// The crypto store layer is caching olm sessions for a given device.
+    /// When used in a multi-process context this cache will get outdated.
+    /// If the machine is used by another process, the cache must be invalidating when the
+    /// main process is resumed.
     pub async fn clear_crypto_cache(&self) {
         self.runtime.block_on(self.inner.clear_crypto_cache())
     }