06d7dc5c3a890f0a141de4cf6f421fe766d99ec3 doc(bdk): Update bdk README (vmammal)
Pull request description:
fixes#1044
### Notes
The code snippet is a compile fail because variables `txout` and `outpoint` are not initialized. Any other suggestions are welcome.
There is still some old commented code in the file that's probably not needed unless we want to provide another example snippet, say for getting new address info.
* [x] Fix broken links
* [x] Use a new unused tprv
* [ ] Try to make persistence example make sense, or maybe just do away with it
#### All Submissions:
* [x] I've signed all my commits
* [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
* [x] I ran `cargo fmt` and `cargo clippy` before committing
ACKs for top commit:
evanlinjin:
ACK 06d7dc5c3a890f0a141de4cf6f421fe766d99ec3
Tree-SHA512: 09a671bc6bea574d7a4b42b64718380ee71a0c5d36c6b7ca1dc19a2c567de510b27ccc91fe05e7178bf31c562db66bc64f660415de5bb2f32f369b13c44ad3d2
a837cd349b