Add fixes for publishing to crates.io

[notmandatory]

Description

To publish the bdk_chain crate I had to either fix the relative reference or create a local README. I decided to add a local README where we can put more detailed docs about bdk_chain. I also had to remove a keyword (max allowed is 5) and add a description to the cargo meta data for bdk_file_store.

Notes to the reviewers

For now the README is just a stub to be filled in later. I already merged this change into the release/1.0.0-alpha branch so I could get the alpha.0 release out today but I'm open to other solutions for the next alpha.1 release.

Changelog notice

None

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

[rajarshimaitra]

ACK 5a090fa

I will try to add more info the chain readme later. For now this is good to go..