Typo fix to the programming guide in the docs

Typo fix to the programming guide in the docs. Changed the word "distibuted" to "distributed".

Author: Cesar Arevalo <cesar@zephyrhealthinc.com>

Closes #1495 from cesararevalo/master and squashes the following commits:

0c2e3a7 [Cesar Arevalo] Typo fix to the programming guide in the docs
(cherry picked from commit 0d01e85f42f3c997df7fee942b05b509968bac4b)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>