status of subdirectories in project READMEs

[hxrts]

I've had a few people ask me about the rust transaction builder and I've pointed them to this repo, however if the readme for that project said a little more about what's currently supported/unsupported and maturity I think that may help newbies.

[tac0turtle]

We should also add docs on how to use this repo, some examples would go a long way.

When we get some short examples we can work on rendering it on the docs.cosmos.network site.

[tony-iqlusion]

I'll add usage docs after I have an end-to-end test written and know it actually works 😉

[tony-iqlusion]

#150 unifies the README.md and toplevel rustdoc, so it's a bit less barebones.

Please check the v0.3.0 release documentation (once I cut it) and let me know if you have further suggestions.

It's still not great but it's hopefully better than it was.