move "Labrador Developer Documentation" from Google drive to GH repository and update content

[mi-hol]

evolve into a "how to" guide later

@EspoTek checking the Wiki I found a link to Labrador Developer Documentation Would you mind to move it to our GH repo?

Update: The challenge for me are the 2 embedded images in "Assembling". They are represented in markdown as [image1]: <data:image/png;base64, encoded strings. Maybe you still have them as files?

I was now comparing the images with my actual board and noticed major differences. Looks like several revisions of board need pictures & references

Originally posted by @mi-hol in #343