Documentation for setting up a local chain as a developer

[james-chf]

The local chain should

• run a single genesis validator node by default (as does the devchain made when using ANOMA_DEV=true)
• have a faucet just like our testnets
• work with our user guide - ie it should have predefined any tokens that may be used in the guide, like XAN

[james-chf]

I've rescoped this ticket to just be about setting up a local chain that would be useable with our current starter documentation i.e. our user guide. Will continue experimenting in https://github.com/anoma/devchain-container with how to most easily set up a local chain after v0.6.1 release

[cwgoes]

@bengtlofgren we should include this in the docs at some point (but low priority)

[james-chf]

Related, working on sharing a script I'm using locally (build_network.sh) in this PR - anoma/devchain-container#8 - that can configure a local Namada chain