Improve docs and examples links on main readme

[alamb]

Which issue does this PR close?

Related to #1613

Rationale for this change

Make it easier to find crates.io, docs.rs and examples from the main arrow crate readme

What changes are included in this PR?

See rendered version https://github.com/alamb/arrow-rs/tree/alamb/main_readme/arrow

[codecov-commenter]

Codecov Report

Merging #1614 (8e9e74d) into master (5374289) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 8e9e74d differs from pull request most recent head f2bf3b8. Consider uploading reports for the commit f2bf3b8 to get more accurate results

@@            Coverage Diff             @@
##           master    #1614      +/-   ##
==========================================
- Coverage   82.90%   82.89%   -0.01%     
==========================================
  Files         193      193              
  Lines       55464    55464              
==========================================
- Hits        45980    45979       -1     
- Misses       9484     9485       +1     

Impacted Files	Coverage Δ
arrow/src/array/transform/mod.rs	86.35% <0.00%> (-0.12%)	⬇️

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