docs: Update README

[ianlewis]

Description:

Update the README to reorder some of the sections, add a "Features" section, and add a section on installing as a Go tool dependency.

Related Issues:

Fixes #1640
Fixes #1655

Checklist:

• Review the CONTRIBUTING.md documentation.
• Add a reference to a related issue in the repository.
• Add a description of the changes proposed in the pull request.
• Add unit tests if applicable.
• Update documentation if applicable.
• Add a note in the CHANGELOG.md if applicable.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.61%. Comparing base (2df3e8b) to head (e086950).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1665   +/-   ##
=======================================
  Coverage   76.61%   76.61%           
=======================================
  Files          20       20           
  Lines        1364     1364           
=======================================
  Hits         1045     1045           
  Misses        233      233           
  Partials       86       86           

Files with missing lines	Coverage Δ
cmd/todos/app.go	85.61% <100.00%> (ø)

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