man: Document abitable in dpkg-architecture(1)

debian/changelog

@@ -10,6 +10,7 @@ dpkg (1.18.2) UNRELEASED; urgency=low
     - Clarify when some features where added in man pages.
     - Document --yet-to-unpack, --predep-packages and all --assert-<feature>
       commands as supported in both «dpkg --help» and dpkg(1).
+    - Document abitable in dpkg-architecture(1).
 
   [ Updated programs translations ]
   * Dutch (Frans Spiesschaert). Closes: #789097

man/dpkg-architecture.1

@@ -223,6 +223,9 @@ Table of known operating system names and mapping to their GNU name.
 .I /usr/share/dpkg/triplettable
 Mapping between Debian architecture triplets and Debian architecture
 names.
+.TP
+.I /usr/share/dpkg/abitable
+Table of Debian architecture ABI attribute overrides.
 .SS Packaging support
 .TP
 .I /usr/share/dpkg/architecture.mk