Moved section on licensing of contributions (fixes pybind#1109) (pybind#1188)

Author: wjakob

CONTRIBUTING.md

@@ -30,8 +30,18 @@ adhere to the following rules to make the process as smooth as possible:
 * This project has a strong focus on providing general solutions using a
   minimal amount of code, thus small pull requests are greatly preferred.
 
-### License
+### Licensing of contributions
 
 pybind11 is provided under a BSD-style license that can be found in the
 ``LICENSE`` file. By using, distributing, or contributing to this project, you
 agree to the terms and conditions of this license.
+
+You are under no obligation whatsoever to provide any bug fixes, patches, or
+upgrades to the features, functionality or performance of the source code
+("Enhancements") to anyone; however, if you choose to make your Enhancements
+available either publicly, or directly to the author of this software, without
+imposing a separate written license agreement for such Enhancements, then you
+hereby grant the following license: a non-exclusive, royalty-free perpetual
+license to install, use, modify, prepare derivative works, incorporate into
+other computer software, distribute, and sublicense such enhancements or
+derivative works thereof, in binary and source code form.

LICENSE

@@ -25,12 +25,5 @@ CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-You are under no obligation whatsoever to provide any bug fixes, patches, or
-upgrades to the features, functionality or performance of the source code
-("Enhancements") to anyone; however, if you choose to make your Enhancements
-available either publicly, or directly to the author of this software, without
-imposing a separate written license agreement for such Enhancements, then you
-hereby grant the following license: a non-exclusive, royalty-free perpetual
-license to install, use, modify, prepare derivative works, incorporate into
-other computer software, distribute, and sublicense such enhancements or
-derivative works thereof, in binary and source code form.
+Please also refer to the file CONTRIBUTING.md, which clarifies licensing of
+external contributions to this project including patches, pull requests, etc.