Merge bitcoindevkit/bdk-cli#104: Update crate documentation

f8a5999289fd0c648b6c18b7f0011339ecaa736d Minor grammar and puctuation fixes (Steve Myers)
e7b6854a67a2419b653a85c04373cbe36f29f62f Update with Readme fixes (rajarshimaitra)
52e8c61392ebbf7895c7da2f5b652972ff4171ed Add all `possible_values` to network command option (Leonardo Lima)
179618ccab40902fbaf2f6710d7ba4307ee2a211 Update crate documentation (rajarshimaitra)

Pull request description:

  ### Description

  After #99 the previous documentation have been removed and new docs as per `structopts` documentation. This PR adds more documentation across the crate..

  This PR is above #102 , to accommodate all the further refactoring changes.

  The Readme About section have been updated with more details.. Readme format made aligned with the BDK project itself..

  The Readme file is used itself as the crate level documentation in docs.rs too..

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk-cli/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  notmandatory:
    ACK f8a5999289fd0c648b6c18b7f0011339ecaa736d

Tree-SHA512: 26c5b3903b0215aa9841c4d1079bbdeb9f9d9d458c7e27dddb625db24eb364b73ca978bb2018f486215878f3601b5572ca58d5c202cb74325c992f3e7107d850