Add license for bibliographic data (second 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 747738804a ("Add license for
bibliographic data"), but unfortunately later reverted in
59b2a5ca15 ("Revert "Add license for bibliographic data"",
https://github.com/xsf/xeps/pull/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: https://github.com/ietf-tools/bibxml-service/issues/302#issuecomment-1274686153

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)