Merge branch 'jn/reftable-doc' into next

Doc update, in preparation for adding the reftable feature.

* jn/reftable-doc:
  reftable: file format documentation

Author: gitster

Documentation/Makefile

@@ -92,6 +92,7 @@ TECH_DOCS += technical/protocol-capabilities
 TECH_DOCS += technical/protocol-common
 TECH_DOCS += technical/protocol-v2
 TECH_DOCS += technical/racy-git
+TECH_DOCS += technical/reftable
 TECH_DOCS += technical/send-pack-pipeline
 TECH_DOCS += technical/shallow
 TECH_DOCS += technical/signature-format