getvar: move docs to --help

getvar

@@ -1,8 +1,21 @@
 #!/usr/bin/env python3
 import common
-parser = common.get_argparse(
-    argparse_args={'description':'https://github.com/cirosantilli/linux-kernel-module-cheat#getvar'}
-)
+parser = common.get_argparse(argparse_args={
+    'description':'''Print the value of a common.py variable.
+
+This is useful to:
+
+* give dry commands on the README that don't change when we refactor directory structure
+* create simple bash scripts that call use common.py variables
+
+For example, to get the Buildroot output directory for an ARM build, use:
+
+....
+./%(prog)s -a arm buildroot_out_dir
+....
+
+'''
+})
 parser.add_argument('variable')
 args = common.setup(parser)
 print(getattr(common, args.variable))