Add a LICENSE.spdx file for automatic license identification

Author: pablogsal

LICENSE.spdx

@@ -0,0 +1,13 @@
+SPDXVersion: SPDX-2.3
+DataLicense: CC0-1.0
+PackageName: CPython
+PackageDownloadLocation: https://github.com/python/cpython
+PackageHomePage: https://www.python.org/
+PackageLicenseConcluded: Python-2.0
+PackageLicenseDeclared: Python-2.0
+PackageLicenseInfoFromFiles: Python-2.0
+FileName: ./LICENSE
+SPDXID: SPDXRef-License-File
+FileType: TEXT
+LicenseConcluded: Python-2.0
+LicenseInfoInFile: Python-2.0