docs: Add conda install instructions and clarity on where to use GT in README.md

[rich-iannone]

This PR addresses two recommendations from the pyOpenSci review of Great Tables. The first involves adding conda installation information. This has been added to README.md

Fixes: #528

The second recommendation involves adding clarity on where GT code should be run (i.e., mostly in a notebook environment or in a Quarto doc). The README.md has been changed to address this in two paragraphs.

Fixes: #530

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.79%. Comparing base (925fa41) to head (5b320f8).
Report is 3 commits behind head on main.

Additional details and impacted files

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##             main     #552   +/-   ##
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  Coverage   89.79%   89.79%           
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  Files          45       45           
  Lines        5321     5321           
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  Hits         4778     4778           
  Misses        543      543           

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[machow]

This seems like a reasonable compromise between showing a table quickly, and making sure people know they need to use .show() if they're in a console. Down the road, we could always make a dedicated "Displaying tables" page in the guide, etc..