README.md - Add a note about threadsafety

Author: chmorgan

README.md

@@ -9,6 +9,8 @@
 
 NimBLE CPP library for use with ESP32 that attempts to maintain compatibility with the [nkolban cpp_utils BLE API](https://github.com/nkolban/esp32-snippets/tree/master/cpp_utils).
 
+The library is threadsafe, characteristics can be set from any thread.
+
 **An Arduino version of this library, including NimBLE, can be [found here.](https://github.com/h2zero/NimBLE-Arduino)**
 
 This library **significantly** reduces resource usage and improves performance for ESP32 BLE applications as compared