doc: Document machine JSON format
doc: Document machine JSON format

We moved machines.json into /etc and a directory because we want it to
be a public API. Don't document the "avatar" property for now, as it
does not really work right now.

Reviewed-by: Stef Walter <8a7fbf0f15d3ad982af54ef28f5c117d2494b76c@redhat.com>

xhad/cockpit,moraleslazaro/cockpit,Scribery/cockpit,deryni/cockpit,deryni/cockpit,stefwalter/cockpit,petervo/cockpit,andreasn/cockpit,stefwalter/cockpit,larskarlitski/cockpit,stefwalter/cockpit,mvollmer/cockpit,garrett/cockpit,dperpeet/cockpit,moraleslazaro/cockpit,harishanand95/cockpit,harishanand95/cockpit,cockpituous/cockpit,Scribery/cockpit,SotolitoLabs/cockpit,cockpituous/cockpit,harishanand95/cockpit,xhad/cockpit,cockpituous/cockpit,larsu/cockpit,larsu/cockpit,dperpeet/cockpit,michalskrivanek/cockpit,deryni/cockpit,larsu/cockpit,martinpitt/cockpit,Scribery/cockpit,petervo/cockpit,Scribery/cockpit,mvollmer/cockpit,SotolitoLabs/cockpit,mvollmer/cockpit,deryni/cockpit,xhad/cockpit,larsu/cockpit,dperpeet/cockpit,moraleslazaro/cockpit,mareklibra/cockpit,Scribery/cockpit,andreasn/cockpit,larskarlitski/cockpit,harishanand95/cockpit,SotolitoLabs/cockpit,cockpituous/cockpit,dperpeet/cockpit,mareklibra/cockpit,dperpeet/cockpit,cockpituous/cockpit,dperpeet/cockpit,stefwalter/cockpit,martinpitt/cockpit,michalskrivanek/cockpit,martinpitt/cockpit,Scribery/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,harishanand95/cockpit,martinpitt/cockpit,larskarlitski/cockpit,stefwalter/cockpit,cockpit-project/cockpit,garrett/cockpit,petervo/cockpit,michalskrivanek/cockpit,mareklibra/cockpit,michalskrivanek/cockpit,larsu/cockpit,Scribery/cockpit,garrett/cockpit,harishanand95/cockpit,petervo/cockpit,cockpit-project/cockpit,garrett/cockpit,andreasn/cockpit,petervo/cockpit,andreasn/cockpit,andreasn/cockpit,larskarlitski/cockpit,deryni/cockpit,cockpit-project/cockpit,xhad/cockpit,mvollmer/cockpit,mareklibra/cockpit,moraleslazaro/cockpit,larskarlitski/cockpit,stefwalter/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,stefwalter/cockpit,SotolitoLabs/cockpit,deryni/cockpit,michalskrivanek/cockpit,martinpitt/cockpit,petervo/cockpit,cockpituous/cockpit,SotolitoLabs/cockpit,michalskrivanek/cockpit,larskarlitski/cockpit,xhad/cockpit,garrett/cockpit,moraleslazaro/cockpit,andreasn/cockpit,michalskrivanek/cockpit,mareklibra/cockpit,xhad/cockpit,deryni/cockpit,andreasn/cockpit,SotolitoLabs/cockpit,larskarlitski/cockpit,mareklibra/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,mareklibra/cockpit,larsu/cockpit,xhad/cockpit,petervo/cockpit,harishanand95/cockpit,dperpeet/cockpit