Update README with development timeline

[codecov-commenter]

Codecov Report

Merging #164 (e6b0edb) into master (0615e7d) will increase coverage by 4.96%. The diff coverage is n/a.

:mega: This organization is not using Codecov’s GitHub App Integration. We recommend you install it so Codecov can continue to function properly for your repositories. Learn more

@@            Coverage Diff             @@
##           master     #164      +/-   ##
==========================================
+ Coverage   59.46%   64.43%   +4.96%     
==========================================
  Files           8        9       +1     
  Lines         264      568     +304     
==========================================
+ Hits          157      366     +209     
- Misses        107      202      +95     

Impacted Files	Coverage Δ
bdk_chain/src/sparse_chain.rs	78.12% <0.00%> (-0.45%)	:arrow_down:
bdk_chain/src/chain_data.rs	48.41% <0.00%> (-0.24%)	:arrow_down:
bdk_chain/src/keychain/keychain_txout_index.rs	0.00% <0.00%> (ø)
bdk_chain/src/file_store.rs	18.18% <0.00%> (ø)
bdk_chain/src/tx_graph.rs	78.15% <0.00%> (+13.70%)	:arrow_up:
bdk_chain/src/keychain.rs	53.57% <0.00%> (+53.57%)	:arrow_up:
bdk_chain/src/chain_graph.rs	75.00% <0.00%> (+75.00%)	:arrow_up:

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[notmandatory]

For todo checkboxes on line 29-35 you should start each line with a dash and space and then the bracket space bracket:

- [ ] like this

[notmandatory]

This looks great and will come in very handy next week for our on-site chats with the Spiral/LDK team. I hope you don't mind if I pull some of this info into slides (with a link back to this README).

[notmandatory]

Was there some TODO work left for the file based persistence module ? I think Monday you mentioned something you were still working on there.