patman: Use less for help file, if available

It's convenient to be able to scroll up in `patman -H`.

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/main.py b/tools/patman/main.py
index 4e0a353..04e37a5 100755
--- a/tools/patman/main.py
+++ b/tools/patman/main.py
@@ -9,6 +9,7 @@
 from argparse import ArgumentParser
 import os
 import re
+import shutil
 import sys
 import traceback
 import unittest
@@ -171,6 +172,8 @@
     elif args.full_help:
         pager = os.getenv('PAGER')
         if not pager:
+            pager = shutil.which('less')
+        if not pager:
             pager = 'more'
         fname = os.path.join(os.path.dirname(os.path.realpath(sys.argv[0])),
                              'README')