README.source: Document convention for bracketted prefixes in changelog

debian/README.source

@@ -89,6 +89,9 @@ Aside from those general rules:
     + Build fixes for configurations that we don't use
     + Fixes for lockdep false positives
 
+If you have time, please add bracketted prefixes to the upstream
+change list as described below under "Changelog conventions".
+
 Applying patches to the Debian kernel tree
 ==========================================
 
@@ -108,6 +111,25 @@ make -f debian/rules source
 
 The resulting source can be found below debian/build.
 
+Changelog conventions
+=====================
+
+If a change only affects some architectures, flavours or featuresets,
+this should be noted with a bracketted prefix on the changelog line:
+
+* [<fset>] Change to featureset <fset>
+* [<arch>] Change that affects Debian architecture <arch>
+* [<arch1>,<arch2>...] Change that affects Debian architectures
+  <arch1>, <arch2>, ...
+* [<arch>/<flavour>] Change that affects kernel flavour <flavour>
+  on Debian architecture <arch>
+* [<arch>/{<flavour1>,<flavour2>...}] Change that affects kernel
+  flavours <flavour1>, <flavour2>, ... on Debian architecture <arch>
+
+You can use wildcards to cover multiple values, e.g. 'arm*' for armel,
+armhf and arm64 architectures.  Also 'x86' is used to cover the Debian
+architectures amd64, i386 and x32.
+
 Kernel config files
 ===================
 Configuration files are constructed dynamically from a number of config