make: add explanation and reference to .deb file format

Makefile

@@ -15,7 +15,8 @@ dist-deb:
 	bazel build //dist:deb_all
 	mkdir -p deb; rm -f deb/*;
 	@ # Bazel cannot include the version in the filename.
-	@ # Extract the version from the .deb files and expand the "__" in the filename to "_<version>_".
+	@ # Extract the version from the .deb "control" manifest and expand the "__" in the filename to "_<version>_".
+	@ #   See e.g. https://en.wikipedia.org/wiki/Deb_(file_format)#Control_archive
 	@for f in `bazel cquery //dist:deb_all --output=files 2>/dev/null`; do \
 		if [ -f "$$f" ]; then \
 			bf=`basename $$f`; \