New docs/openbazaar.1

A new `docs/openbazaar.1`

The content is from [openbazaar.1](https://github.com/OpenBazaar/OpenBazaar/blob/90b8f1748627a11f76f0bd3e57606e71ec0897c6/docs/openbazaar.1) and `openbazaar help`.

NOTES:
- `openbazaar help` content come from [OpenBazaar Beta 3.0](https://github.com/OpenBazaar/OpenBazaar/tree/v0.3.0).
- Please check the content carefully.