Add the CREDITS file

This is a file with ... credits, yes :) While implementing the C/R stuff
we've receive a LOT of help from various people and would like to mention
them. If we've undeservedly forgotten someone (or something) -- please
help us to make amends and send a patch to this file.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

CREDITS

+The following people provided invaluable help to CRIU project
+(in alphabetical order)
+-------------------------------------------------------------------
+
+Andrew Morton
+David Miller
+Eric Dumazet
+Eric W. Biederman
+H. Peter Anvin
+Kees Cook
+KOSAKI Motohiro
+Li Yu
+Linus Torvalds
+Oleg Nesterov
+Serge Hallyn
+Tejun Heo