replace the readme example with a dialog example

[altendky]

No description provided.

[codecov]

Codecov Report

Merging #185 (51e3c04) into master (0520841) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master      #185    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           25        29     +4     
  Lines         1387      1500   +113     
  Branches        77        77            
==========================================
+ Hits          1387      1500   +113     

Impacted Files	Coverage Δ
qtrio/_tests/examples/readme/test_qt.py	100.00% <100.00%> (ø)
qtrio/_tests/examples/readme/test_qtrio.py	100.00% <100.00%> (ø)
qtrio/examples/readme/qt.py	100.00% <100.00%> (ø)
qtrio/examples/readme/qtrio.py	100.00% <100.00%> (ø)

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