Update Mikrotik Hyperlink based on Mikrotik's Guidance

[jtholm2]

Link to relevant section of the documentation: https://github.com/GoogleCloudPlatform/terraformer/blob/master/docs/mikrotik.md?plain=1#L1C25-L1C66

The hyperlink included here points to a page that states There is currently no text in this page. Additionally, the main page of the MikroTik website states that the wiki.mikrotik.com page is no longer being updated and that users should refer to https://help.mikrotik.com/docs/. This information is shown in the screenshots below.

Screenshot 1:

Screenshot 2:

If the project maintainers are ok with me sending a PR to update the documentation hyperlink, I would love to do so!