dpkg-maintscript-helper: Unify somewhat --help output with other commands

debian/changelog

@@ -132,6 +132,7 @@ dpkg (1.16.1) UNRELEASED; urgency=low
     - Correctly format text with bold and italics.
   * Refer to Sources and Packages files as part of a repository instead of
     as being of exclusive use or owned by APT, which has never been the case.
+  * Unify somewhat dpkg-maintscript-helper --help output with other commands.
 
   [ Bill Allombert]
   * Add support for Build-Features: build-arch. Closes: #229357

scripts/dpkg-maintscript-helper.sh

@@ -234,22 +234,16 @@ warning() {
 
 usage() {
 	cat <<END
-Syntax: $0 <command> <parameters> -- <maintainer script parameters>
-
-Commands and parameters:
+Usage: $PROGNAME <command> <parameter>... -- <maintainer-script-parameter>...
 
+Commands:
   supports <command>
-	Returns 0 (success) if the given command is supported, 1
-	otherwise.
-
+	Returns 0 (success) if the given command is supported, 1 otherwise.
   rm_conffile <conffile> [<last-version> [<package>]]
-	Remove obsolete conffile.
-	Must be called in preinst, postinst and postrm.
-
+	Remove obsolete conffile. Must be called in preinst, postinst and
+	postrm.
   mv_conffile <old-conf> <new-conf> [<last-version> [<package>]]
-	Rename a conffile.
-	Must be called in preinst, postinst and postrm.
-
+	Rename a conffile. Must be called in preinst, postinst and postrm.
   help
 	Display this usage information.
 END