Update README.md

[alexzhaohong]

• Add screenshot images
• Add installation section
• Edit copy

[alexzhaohong]

Before:

After:

[alexzhaohong]

I also have a screenshot of Jaws of the Lion scenario 1 if having four characters in Gloomhaven is too confusing.

[codecov-commenter]

Codecov Report

Merging #167 (dc6c512) into main (579757d) will not change coverage. The diff coverage is n/a.

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@@          Coverage Diff          @@
##            main    #167   +/-   ##
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  Coverage   1.00%   1.00%           
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  Files        134     134           
  Lines       9333    9333           
=====================================
  Hits          94      94           
  Misses      9239    9239           

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