docs: update README for JSR

[iuioiua]

This change trims some of the README, by relying more on JSR's usage instructions built-in to package pages.

My thinking is that JSR already does a fine job at instructing the reader on how to use the package and further usage instructions simply aren't needed elsewhere. This should also act as more of a forcing function to improve our documentation.

I'd like to complete remove the packages table once jsr-io/jsr#421 is merged, so there's no need to maintain such a list. We can instead have a note on each package's module documentation like so:

/**
 * This module does this and that.
 *
 * Note: this module is unstable and may change in the future.
 * @module
 */

and

/**
 * This module does this and that.
 *
 * Note: this module is settled and is unlikely to change in the future.
 * @module
 */

Supercedes #4652

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.36%. Comparing base (3155f00) to head (c99c495).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4654   +/-   ##
=======================================
  Coverage   91.36%   91.36%           
=======================================
  Files         477      477           
  Lines       37334    37334           
  Branches     5325     5325           
=======================================
  Hits        34109    34109           
  Misses       3164     3164           
  Partials       61       61           

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[kt3k]

LGTM