Add .reuse/dep5 for full REUSE compliance.

This includes explicit reference to each file which currently lack (or
cannot themselves contain) a license comment preamble. This is primarily
to avoid the addition of several `.license` files per licensable file.

.reuse/dep5

@@ -0,0 +1,7 @@
+Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
+Upstream-Contact: Digital Bazaar, Inc. <support@digitalbazaar.com>
+
+Files: *.md .gitignore .npmrc package.json test/.npmrc test/mocha/.eslintrc
+    test/package.json
+Copyright: 2012-2024 Digital Bazaar, Inc.
+License: BSD-3-Clause