message: README: add note about linking to thread lib
  pthread is included in glibc and therefore it is required to link not
  only to libdronelink.a but also pthread.
diff: @@ -41,6 +41,8 @@ Or, to install the files system-wide, using:
  INSTALL_PREFIX=/usr/local make default install
  ```
  +Note that when using the library `libdronelink.a`, you need to link to a thread library such as pthread on a POSIX system. (pthread is not included in the static library because it is included in glibc.)
  +
  ## Example
  Check out the [example](example/). It sets up a UDP connection, waits for a device appearing, and commands it to takeoff and land again, while receiving some telemetry.
  @@ -62,6 +64,8 @@ cmake ..
  make && ./takeoff_and_land
  ```
  +Note that the example needs to be linked to a thread library (see [CMakeLists.txt](example/CMakeLists.txt))
  +
  ## License
  The DroneLink SDK is licensed under the permissive BSD 3-clause, see [LICENSE.md](LICENSE.md).
  