message: core: improve docstring
diff: @@ -109,8 +109,7 @@ public:
  using IsConnectedCallback = std::function<void(bool)>;
  /**
  - * @brief Subscribe to callback to be called when system is discovered
  - * or times out.
  + * @brief Subscribe to callback to be called when system connection state changes.
  *
  * @param callback Callback which will be called.
  */
  