A+C: Add information about my contributions

As requested by @cznic add information about me and my company to
AUTHORS and CONTRIBUTORS.

Btw, I'm not a lawyer and maybe there are country differences, but I
used to think that:

- author is the person who actually creates the work.
- copyright holder is who owns the copyright on that work (i.e. the
  person, or company he is working for or someone else).

The `AUTHORS` file however gets it the other way - it says to put there
information about who is "copyright holder" which goes counterwise above
classification.

----

I understand however that the exact A+C approach is taken from the Go
project so let's also continue following it here.

AUTHORS

@@ -9,3 +9,4 @@
 # Please keep the list sorted.
 
 Jan Mercl <0xjnml@gmail.com>
+Nexedi <jp@nexedi.com>

CONTRIBUTORS

@@ -10,4 +10,5 @@ Andrey Elenskiy <andrey.elenskiy@gmail.com>
 Brian Fallik <bfallik@gmail.com>
 Dan Kortschak <dan.kortschak@adelaide.edu.au>
 Jan Mercl <0xjnml@gmail.com>
+Kirill Smelkov <kirr@nexedi.com>
 Nikifor Seryakov <nikandfor@gmail.com>