jcs: Add usage for jcs install

scripts/jcs

@@ -1773,7 +1773,26 @@ is created.
 --<<<-- usage snapshot --
 
 -->>>-- usage install --
-usage: jcs install .inf-file [-h] [-f] [-b backup-dir]
+
+jcs install installs files according to an installation
+description in a .inf file
+
+	usage:
+		jcs install .inf-file [-h] [-f|-t] [-b backup-dir]
+
+	-b dir:	make a backup into directory dir
+
+	-f:	force an installation, irrespective of the
+		files' modification dates. If this option
+		is not present, jcs overwrites destination files
+		only when the source file is newer than the
+		destination
+
+	-p prefix: prepend target directories with prefix
+
+	-t:	test mode (don't actually install anything, but log
+		what would be installed)
+
 --<<<-- usage install --
 
 -->>>-- usage smake --