patman: Handle creation of patman config file

patman shouts when it couldn't find a $(HOME)/.patman file.
Handle it in a sane way by creating a new one for the user.
It looks for a user.name and user.email in the global .gitconfig
file, waits for the user input if it can't find there. Update the
same in the README

Signed-off-by: Vikram Narayanan <vikram186@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
Cc: Simon Glass <sjg@chromium.org>
Cc: Wolfgang Denk <wd@denx.de>
diff --git a/tools/patman/README b/tools/patman/README
index 1af8665..86ede78 100644
--- a/tools/patman/README
+++ b/tools/patman/README
@@ -68,6 +68,9 @@
 For most cases patman will locate and use the file 'doc/git-mailrc' in
 your U-Boot directory. This contains most of the aliases you will need.
 
+During the first run patman creates a config file for you by taking the default
+user name and email address from the global .gitconfig file.
+
 To add your own, create a file ~/.patman like this:
 
 >>>>