inline jiter README to fixup sdist build

[davidhewitt]

The README.md is a duplication of the root README, with some additional links added in. Think it makes sense to just inline it in this case.

[codspeed-hq]

CodSpeed Performance Report

Merging #168 will not alter performance

_{Comparing dh/fix-sdist (1159502) with main (f970f0b)}

Summary

✅ 73 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.92%. Comparing base (f970f0b) to head (1159502).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #168   +/-   ##
=======================================
  Coverage   88.92%   88.92%           
=======================================
  Files          13       13           
  Lines        2195     2195           
  Branches     2195     2195           
=======================================
  Hits         1952     1952           
  Misses        148      148           
  Partials       95       95           

Files with missing lines	Coverage Δ
crates/jiter/src/lib.rs	93.33% <ø> (ø)

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