Added related Configuration information in Xamarin.Forms.Maps Namespace doc

[jsuarezruiz]

There is a detailed document with Map initialization and configuration information. In the definition of the Map namespace, this PR adds a link to that documentation.

fix #152

[opbld34]

Docs Build status updates of commit aed2f21:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/ns-Xamarin.Forms.Maps.xml	✅Succeeded

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