chore: add import ordering rule

[voidash]

Description

Following import order will be enforced by rustfmt with StdExternalCrate on rustfmt

1. std, core
2. external crate
3. self, super, crate import

contributing.md is now a different file

Type of Change

• Chore

Checklist

• I have performed a self-review of my code.
• I have commented my code where necessary.
• I have updated the documentation if needed.
• My changes do not introduce new warnings.
• I have added tests that prove my changes are effective or that my feature works.
• New and existing tests pass with my changes.

Related Issues

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.91%. Comparing base (6d4bd56) to head (493d9d3).
Report is 7 commits behind head on master.

@@            Coverage Diff             @@
##           master     #255      +/-   ##
==========================================
- Coverage   57.94%   57.91%   -0.03%     
==========================================
  Files         119      119              
  Lines       13425    13425              
==========================================
- Hits         7779     7775       -4     
- Misses       5646     5650       +4     

Files	Coverage Δ
crates/btcio/src/broadcaster/handle.rs	0.00% <ø> (ø)
crates/btcio/src/broadcaster/task.rs	86.71% <ø> (ø)
crates/btcio/src/reader/query.rs	0.00% <ø> (ø)
crates/btcio/src/rpc/client.rs	0.00% <ø> (ø)
crates/btcio/src/rpc/types.rs	80.32% <ø> (ø)
crates/btcio/src/status.rs	0.00% <ø> (ø)
crates/btcio/src/writer/broadcast.rs	0.00% <ø> (ø)
crates/btcio/src/writer/builder.rs	95.63% <ø> (ø)
crates/btcio/src/writer/config.rs	0.00% <ø> (ø)
crates/btcio/src/writer/utils.rs	86.53% <ø> (ø)
... and 70 more

... and 1 file with indirect coverage changes

[Rajil1213]

Looks good now.