documentation

Pull request #1909: feature/ZBX-24521-7.0-D3. Added footnote to StartDiscoverers parameter description; refined file descriptors-related info.

Merge in WEB/documentation from feature/ZBX-24521-7.0-D3 to release/7.0

* commit '5402523094aab11972e5fcc698311938368ebf5f':
  [ZBX-24521] updated wording, added line break in note
  [ZBX-24521] added footnote to StartDiscoverers parameter description
  [ZBX-24521] refined wording, grammar, sentence structure, added helpful links
  [ZBX-24521] made line breaks useful and pretty