10b4b6c665d58321436413d1d9c0486e7d74c5ec Documentations regarding absolute_fee and fee_rate updated (TATHAGATA ROY)
Pull request description:
### Description
This pr solves this issue #856
Updated the documentation for absolute fee and fee rate in BDK docs
#### All Submissions:
* [x] I've signed all my commits
* [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
#### Bugfixes:
* [x] I'm linking the issue being fixed by this PR
ACKs for top commit:
danielabrozzoni:
ACK 10b4b6c665d58321436413d1d9c0486e7d74c5ec
Tree-SHA512: 5b5f360b742313443368dc0b75275c38888cb358545661f7d9c78f3290789c50ffa9830e18473055d8e3da544c7d9527b023a1acdb28eaf862b24c892b23e9c4