Add license to manifest

Author: lmcinnes

MANIFEST.in

@@ -1,4 +1,4 @@
-include *.rst *.txt pyproject.toml
+include *.rst *.txt pyproject.toml LICENSE
 recursive-include hdbscan *.py *.pyx *.pxd *.c
 recursive-include notebooks *.ipynb *.npy *.svg
 recursive-include examples *.py