Clarify the license of the included pythoncapi_compat.h header

The `pythoncapi_compat.h` header is distributed under the MIT license,
so include the full text of the license in the header and mention it in
the top level LICENSE file.

Fixes: #64

1 files changed, 1 insertions, 0 deletions

diff --git a/NOTICE b/NOTICE
new file mode 100644
index 0000000..8a796ab
--- /dev/null
+++ b/NOTICE
@@ -0,0 +1 @@
+Copyright 2018-present Contributors to the immutables project.