[jnigen] LICENSE trailer for generated code (https://github.com/dart-lang/jnigen/issues/63)

pkgs/jnigen/LICENSE

diff --git a/pkgs/jnigen/LICENSE b/pkgs/jnigen/LICENSE
index 33474aa..f0604ef 100644
--- a/pkgs/jnigen/LICENSE
+++ b/pkgs/jnigen/LICENSE
@@ -25,3 +25,8 @@
 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.
+
+Code generated by JNIgen is owned by the owner of the input file used
+when generating it. This code is not standalone and requires a
+support library to be linked with it. This support library is itself
+covered by the above license.