Fix Nominatim URL in batch geocode algorithm help

[Geo-Jagaimo]

Description

What I did

• Regarding the processing tool "Batch Nominatim geocoder", the "Nominatim" in the help text was displayed as a link, but the link destination was not set. Therefore, I have added the link destination.

Notes

• I specified https://nominatim.org/ as the link destination, but please let me know if there is a more appropriate link.

[nicogodet]

QGIS organisation uses its own Nominatim instance hosted at https://nominatim.qgis.org.
I think it should be this URL instead of OSM one.

[Geo-Jagaimo]

QGIS organisation uses its own Nominatim instance hosted at https://nominatim.qgis.org. I think it should be this URL instead of OSM one.

Thank you for your comment.
I'll fix it.

[github-actions]

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
(Built from commit fe299d7)

🍎 MacOS Qt6 builds

Download MacOS Qt6 builds of this PR for testing.
This installer is not signed, control+click > open the app to avoid the warning
(Built from commit fe299d7)