Add basic coding guidelines section in DEVELOPMENT

[tidal]

We maintainers want to add basic coding guidelines as an orientation for pull requests and as a reference for reviews.

• Adds basic coding guidelines section with a link to Clean Code PHP
• Moves the examples section back to the main README, as it enjoyed its stay in DEVELOPMENT.md but wants to have a more prominent place again.

[codecov]

Codecov Report

Merging #781 (5da612d) into main (ea5b7c1) will increase coverage by 0.97%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main     #781      +/-   ##
============================================
+ Coverage     78.51%   79.49%   +0.97%     
- Complexity     1337     1407      +70     
============================================
  Files           154      160       +6     
  Lines          3291     3472     +181     
============================================
+ Hits           2584     2760     +176     
- Misses          707      712       +5     

Flag	Coverage Δ
7.4	79.49% <ø> (+0.97%)	⬆️
8.0	79.56% <ø> (+0.96%)	⬆️
8.1	79.56% <ø> (+0.96%)	⬆️

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Impacted Files	Coverage Δ
src/SDK/Trace/ExporterFactory.php	100.00% <0.00%> (ø)
src/SDK/Common/Dsn/Factory.php	100.00% <0.00%> (ø)
src/SDK/Common/Dsn/Dsn.php	90.90% <0.00%> (ø)
src/API/Common/Event/EmitsEventsTrait.php	100.00% <0.00%> (ø)
src/SDK/Common/Otlp/HttpEndpointResolver.php	100.00% <0.00%> (ø)
src/API/Common/Event/Dispatcher.php	100.00% <0.00%> (ø)
src/SDK/Common/Dsn/Parser.php	100.00% <0.00%> (ø)
src/Contrib/OtlpHttp/Exporter.php	94.00% <0.00%> (+1.27%)	⬆️

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