Update README.md to only include high level docs

[wabjnr]

Documentation? Who needs it?

Moving the main docs directly to the Dev Portal.

[predikament]

I think a small code example should still be here, at a minimum;
This would leave any users of the library able to understand it on a superficial level at the very least, then if they want more documentation they can find those externally.

Also I would rather update this to include the new external docs link once we have that ready, instead of updating it now to remove everything and leaving users without a place to find this info in the interim.

[guilleccc]

Just keep in mind @wabjnr that the dev portal documentation is not public, so normal github users won't be able to access it: https://devportal.noriginmedia.com/docs/Norigin-Spatial-Navigation/

[wabjnr]

@guilleccc the Spatial Navigation page, amongst others, is now public, so I have linked to it.

[predikament]

This is OK, but I would still prefer a small concrete usage example to be included here in addition to the external documentation.

Let's see how we can best solve that later then.