Add license for bibliographic data (third attempt)

We were asked [1] to state that the XEP bibliographic data is openly
available and free of charge if we want it to be consumed by third
parties.

This weas previously merged as 7477388 ("Add license for
bibliographic data"), but unfortunately later reverted in
59b2a5c ("Revert "Add license for bibliographic data"",
#1221). However, the fix for the
broken docker build is trivial: simply also copy refs-LICENSE into the
container. This commit does that.

Fixes #1219.

1: ietf-tools/bibxml-service#302 (comment)

Dockerfile

@@ -6,7 +6,7 @@ FROM xmppxsf/xeps-base:latest as build
 ARG NCORES=1
 ARG TARGETS="html inbox-html inbox-xml pdf xeplist refs xml"
 
-COPY *.xml xep.* *.css *.xsl *.js *.xsl Makefile /src/
+COPY *.xml xep.* *.css *.xsl *.js *.xsl Makefile refs-LICENSE /src/
 COPY resources/*.pdf /src/resources/
 COPY tools/*.py /src/tools/
 COPY inbox/*.xml inbox/*.ent inbox/*.dtd /src/inbox/

Makefile

@@ -76,8 +76,11 @@ inbox-xml: $(OUTDIR)/inbox $(proto_xep_xmls)
 .PHONY: pdf
 pdf: $(xep_pdfs)
 
+$(REFSDIR)/LICENSE: refs-LICENSE
+	cp $< $@
+
 .PHONY: refs
-refs: $(xep_refs)
+refs: $(xep_refs) $(REFSDIR)/LICENSE
 
 .PHONY: examples
 examples: $(xep_examples)

refs-LICENSE

@@ -0,0 +1,9 @@
+To the extent possible under law, the XMPP Standards Foundation (XSF)
+has waived all copyright and related or neighboring rights to XSF's
+bibliographic data.
+
+That is, the bibliographic data, which is also accessible via
+https://xmpp.org/extensions/refs/, is put in the public domain via
+CC0 1.0 [1].
+
+1: https://creativecommons.org/publicdomain/zero/1.0/