Contributing guidelines improved

[guedou]

This PR makes some modifications to our guidelines:

• ask to open a Draft PR when the work is incomplete
• remove the paragraph on related to legacy non-PEP08 code

[codecov]

Codecov Report

Merging #2399 into master will decrease coverage by 0.28%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2399      +/-   ##
==========================================
- Coverage   87.67%   87.39%   -0.29%     
==========================================
  Files         242      242              
  Lines       50656    50656              
==========================================
- Hits        44413    44271     -142     
- Misses       6243     6385     +142

Impacted Files	Coverage Δ
scapy/contrib/automotive/obd/scanner.py	6.74% <0%> (-88.77%)	⬇️
scapy/contrib/isotp.py	82.92% <0%> (-6.25%)	⬇️
scapy/contrib/automotive/gm/gmlanutils.py	89.69% <0%> (-2.43%)	⬇️
scapy/contrib/automotive/obd/services.py	93.1% <0%> (-1.73%)	⬇️
scapy/layers/ntp.py	91.51% <0%> (-0.27%)	⬇️
scapy/layers/inet6.py	81.89% <0%> (+0.1%)	⬆️
scapy/layers/inet.py	73.14% <0%> (+0.16%)	⬆️
scapy/contrib/gtp.py	87.15% <0%> (+0.3%)	⬆️
scapy/compat.py	78.2% <0%> (+7.69%)	⬆️

[guedou]

Ready to be merged!

[gpotter2]

Side note but all references to things like

Please label your issues "bug".

Seem outdated. They can't do that. We could potentially use the new GitHub issue templates

[guedou]

@gpotter2 I pushed a new commit that removes the references to github labels.