documentation

Pull request #879: feature/ZBX-22622-7.0-D: Updates regarding custom alert script path validation and macros in media type "Script" parameters (related to ZBXNEXT-6796).

Merge in WEB/documentation from feature/ZBX-22622-7.0-D to release/7.0

* commit '34f4f63b4b93117fc8d3393463387e296579a583':
  [ZBX-22622] Minor update to grammar
  Updated images and info on macros in media type "Script" parameters (related to ZBXNEXT-6796)
  [ZBX-22622] Updated grammar & style; updated images to reflect the script example and description
  [ZBX-22622] Updates regarding custom alert script path validation