copied Wiki page on releasing Trio to doc

[smurfix]

No description provided.

[codecov]

Codecov Report

Merging #598 into master will decrease coverage by 5.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #598      +/-   ##
==========================================
- Coverage   99.31%   94.17%   -5.14%     
==========================================
  Files          91       91              
  Lines       10822    10822              
  Branches      753      753              
==========================================
- Hits        10748    10192     -556     
- Misses         56      582     +526     
- Partials       18       48      +30

Impacted Files	Coverage Δ
trio/_wait_for_object.py	0% <0%> (-100%)	⬇️
trio/_core/_io_epoll.py	0% <0%> (-100%)	⬇️
trio/_core/_windows_cffi.py	0% <0%> (-93.55%)	⬇️
trio/tests/test_wait_for_object.py	9.02% <0%> (-90.98%)	⬇️
trio/_core/_io_windows.py	0% <0%> (-78.29%)	⬇️
trio/_core/tests/test_windows.py	23.33% <0%> (-76.67%)	⬇️
trio/_core/tests/test_epoll.py	27.77% <0%> (-72.23%)	⬇️
trio/hazmat.py	72.72% <0%> (-27.28%)	⬇️
trio/_util.py	86.58% <0%> (-13.42%)	⬇️
trio/_highlevel_open_unix_stream.py	66.66% <0%> (-11.12%)	⬇️
... and 15 more

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[njsmith]

I'm sure this could be refined more, but that can go in future PRs :-). Thanks!