D17801: Update Okular developer documentation

[Yuri Chornoivan]

yurchor marked 3 inline comments as done.

REPOSITORY
  R223 Okular

REVISION DETAIL
  https://phabricator.kde.org/D17801

To: yurchor, #okular
Cc: aacid, ngraham, okular-devel, tfella, darcyshen