The Free On-line Dictionary of Computing (30 December 2018):

doco

    /do'koh/ 1. (In-house jargon at Symbolics) A
   documentation writer.

   See also devo and mango.

   2. (UK) A short technical document.  A "doco" is often not the
   documentation passed to management.

   Compare doc.

   [Jargon File]

   (1999-10-08)