Addition to release checklist in makefile (#43709)

Author: SamuraiAku

Makefile

@@ -127,15 +127,16 @@ release-candidate: release testall
 	@echo 2. Update references to the julia version in the source directories, such as in README.md
 	@echo 3. Bump VERSION
 	@echo 4. Increase SOMAJOR and SOMINOR if needed.
-	@echo 5. Create tag, push to github "\(git tag v\`cat VERSION\` && git push --tags\)"		#"` # These comments deal with incompetent syntax highlighting rules
-	@echo 6. Clean out old .tar.gz files living in deps/, "\`git clean -fdx\`" seems to work	#"`
-	@echo 7. Replace github release tarball with tarballs created from make light-source-dist and make full-source-dist with USE_BINARYBUILDER=0
-	@echo 8. Check that 'make && make install && make test' succeed with unpacked tarballs even without Internet access.
-	@echo 9. Follow packaging instructions in doc/build/distributing.md to create binary packages for all platforms
-	@echo 10. Upload to AWS, update https://julialang.org/downloads and http://status.julialang.org/stable links
-	@echo 11. Update checksums on AWS for tarball and packaged binaries
-	@echo 12. Announce on mailing lists
-	@echo 13. Change master to release-0.X in base/version.jl and base/version_git.sh as in 4cb1e20
+	@echo 5. Update SPDX document by running the script contrib/updateSPDX.jl
+	@echo 6. Create tag, push to github "\(git tag v\`cat VERSION\` && git push --tags\)"		#"` # These comments deal with incompetent syntax highlighting rules
+	@echo 7. Clean out old .tar.gz files living in deps/, "\`git clean -fdx\`" seems to work	#"`
+	@echo 8. Replace github release tarball with tarballs created from make light-source-dist and make full-source-dist with USE_BINARYBUILDER=0
+	@echo 9. Check that 'make && make install && make test' succeed with unpacked tarballs even without Internet access.
+	@echo 10. Follow packaging instructions in doc/build/distributing.md to create binary packages for all platforms
+	@echo 11. Upload to AWS, update https://julialang.org/downloads and http://status.julialang.org/stable links
+	@echo 12. Update checksums on AWS for tarball and packaged binaries
+	@echo 13. Announce on mailing lists
+	@echo 14. Change master to release-0.X in base/version.jl and base/version_git.sh as in 4cb1e20
 	@echo
 
 $(build_man1dir)/julia.1: $(JULIAHOME)/doc/man/julia.1 | $(build_man1dir)