[TASK] Link to crawler extension docs

Change-Id: Ie1e780af0b15c9785225bd8a147b08458b6a3b06
Resolves: #79541
Releases: master
Reviewed-on: https://review.typo3.org/51463


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>