Link to new Discord and several other improvements on Readme

[afontcu]

• [x] Update basic example to use screen
• [x] Add jest-dom and byRole suggestions
• [x] Link to new Discord server
• [x] Add Guiding Principle section
• [x] Add links to issuess

[codecov[bot]]

Codecov Report

Merging #148 into master will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #148   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines           70        70           
  Branches        13        13           
=========================================
  Hits            70        70           

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[afontcu]

:tada: This PR is included in version 5.1.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: