title: How do I explicitly specify an out-of-tree source in CMake?
body: <p>I looked at this post: <a href="https://stackoverflow.com/questions/15569548/using-cmake-to-statically-link-to-a-library-outside-of-the-project">Using CMake to statically link to a library outside of the project</a>.  But I'm still having trouble interpreting what this means:</p>
  
  <pre><code>add_subdirectory(/path/to/the/library/source/directory subproject/grzeslib)
  </code></pre>
  
  <p>I'm assuming "/path/to/the/library/source/directory" means the path from the hard drive, but I don't understand what "subproject/grzeslib" means.
  Now I tried:</p>
  
  <pre><code>include_directories(../path/to/dir)
  add_subdirectory (../path/to/dir .) 
  </code></pre>
  
  <p>But I'm getting an elaborate warning.  Is there a better way to do this?</p>