message: README: add goals of library, minor fixes
diff: ## Description
  -Messaging library/SDK for [PX4 flight stack](http://github.com/PX4/Firmware) using [Mavlink](http://mavlink.org).
  +DroneLink is a SDK for the [PX4 flight stack](http://github.com/PX4/Firmware) using [Mavlink](http://mavlink.org).
  +
  +It is a C++11 library aiming to be:
  +
  +- Easy to use with a simple API.
  +- Fast and lightweight.
  +- Cross-platform (Linux, Mac, Windows, iOS, Android).
  +- Extensible (using compile-time plugins).
  +
  +## Interfacing
  +
  +DroneLink currently takes care of the mavlink messaging using a UDP network connection to the drone. Connecting via TCP, or serial is planned for but not implemeted yet.
  +
  +The library provides both synchronous (blocking) API calls, as well as asynchronous API calls using callbacks.
  ## License
  -BSD 3-clause, see [LICENSE.md](LICENSE.md).
  +The DroneLink SDK is licensed under the permissive BSD 3-clause, see [LICENSE.md](LICENSE.md).
  ## Authors
  @@ -17,6 +30,7 @@ See [AUTHORS.md](AUTHORS.md).
  ### Building
  Make sure the submodules are updated first.
  +
  ```
  git submodule update --init --recursive
  ```
  @@ -77,7 +91,7 @@ cmake ..
  cmake --build .
  ```
  -### Build with external directory for plugins/integration_tests
  +### Build with external directory for plugins and custom integration_tests
  The SDK is split into a [core](core/) and [plugins](plugins/). The plugins are included at compile time.
  The cmake script [autogenerate_plugin_container.cmake](autogenerate_plugin_container.cmake) takes care of including the plugin folders and integrations tests.
  @@ -170,7 +184,7 @@ make run_integration_tests
  Make sure you are connected to a vehicle and check the connection using e.g.
  ```
  -make && build/default/integration_tests_runner --gtest_filter="SitlTest.TelemetrySimple"
  +make && build/default/integration_tests_runner --gtest_filter="SitlTest.TelemetryAsync"
  ```
  Note that some of the tests might not be suited for real vehicles, especially the takeoff and kill test.
  @@ -184,7 +198,7 @@ make && build/default/integration_tests_runner --gtest_list_tests
  To run a single integration test:
  ```
  -make && build/default/integration_tests_runner --gtest_filter="SitlTest.TelemetrySimple"
  +make && build/default/integration_tests_runner --gtest_filter="SitlTest.TelemetryAsync"
  ```
  To run all telemetry tests:
  