Add explainer text

.gitignore

@@ -1 +1,3 @@
 index.html
+README.html
+.*.sw?

Makefile

@@ -0,0 +1,26 @@
+SHELL=/bin/bash
+
+bikeshed_files = index.bs
+
+.PHONY: clean spec
+
+spec: $(bikeshed_files:.bs=.html)
+
+clean:
+	rm -f $(bikeshed_files:.bs=.html) README.html
+
+README.html: README.md
+	pandoc -f gfm --metadata title="Explainer" -s -o $@ $<
+
+%.html: %.bs
+	@ (HTTP_STATUS=$$(curl https://api.csswg.org/bikeshed/ \
+	                       --output $@ \
+	                       --write-out "%{http_code}" \
+	                       --header "Accept: text/plain, text/html" \
+												 -F die-on=warning \
+	                       -F file=@$<) && \
+	[[ "$$HTTP_STATUS" -eq "200" ]]) || ( \
+		echo ""; cat $@; echo ""; \
+		rm -f $@; \
+		exit 22 \
+	);