Move remaining documentation in google docs here (exporter guidelines, client lib etc) #379
Description
Discussed it quickly in IRC: Most people feel the exporter guidelines (https://docs.google.com/document/d/1JapuiRbp-XoyECgl2lPdxITrhm5IyCUq9iA_h6jp3OY/edit#heading=h.pml2liglk52z) should be in the main docs.