UK: get and create organization members team/group
UK: list members in an organization
UK: Add user to an orgnization via the API, closes #281
UK: docs for add user to organization
Merge pull request #293 from onaio/281-add-user-to-org-docs

docs for add user to organization
Merge branch 'master' into 282-add-user-to-team

* master:
  UK: docs for add user to organization
  UK: Add user to an orgnization via the API, closes #281
  UK: list members in an organization
  UK: get and create organization members team/group