documentation

Pull request #1793: feature/ZBXNEXT-8682-6.0-D2. Documented length limit (512KB) for preprocessing test results.

Merge in WEB/documentation from feature/ZBXNEXT-8682-6.0-D2 to release/6.0

* commit '18df4f05fab7a45433b5398110701cd60e6a3375':
  [ZBXNEXT-8682] fixed feature implementation version
  [ZBXNEXT-8682] updated wording
  [ZBXNEXT-8682] updated wording
  [ZBXNEXT-8682] improved grammar, wording
  [ZBXNEXT-8682] documented length limit (512KB) for preprocessing test results