Clarify docs on --strict marks

[Zac-HD]

I've been looking into the behaviour of unknown marks today, and discovered that the docs for the --strict option are a bit misleading: even with --strict, you don't need to list marks in pytest.ini if they come from pytest or are added by a plugin. IMO this is the right thing to do, as --strict is really to catch typos, so I've just fixed the docs.

[codecov]

Codecov Report

Merging #4828 into master will decrease coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4828      +/-   ##
==========================================
- Coverage   95.72%   95.64%   -0.09%     
==========================================
  Files         113      113              
  Lines       25666    25163     -503     
  Branches     2505     2498       -7     
==========================================
- Hits        24570    24068     -502     
+ Misses        773      772       -1     
  Partials      323      323

Flag	Coverage Δ
#linux	95.45% <ø> (-0.09%)	⬇️
#osx	93.29% <ø> (ø)	⬆️
#windows	93.67% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
testing/test_modimport.py	81.81% <0%> (-1.52%)	⬇️
testing/code/test_source.py	95.53% <0%> (-1.07%)	⬇️
testing/test_argcomplete.py	68.11% <0%> (-0.9%)	⬇️
testing/test_compat.py	91.13% <0%> (-0.63%)	⬇️
testing/test_skipping.py	97.65% <0%> (-0.57%)	⬇️
src/_pytest/warnings.py	88.88% <0%> (-0.53%)	⬇️
src/_pytest/debugging.py	77.98% <0%> (-0.41%)	⬇️
src/_pytest/fixtures.py	97.91% <0%> (-0.31%)	⬇️
src/_pytest/logging.py	94.96% <0%> (-0.31%)	⬇️
testing/test_assertrewrite.py	83.55% <0%> (-0.3%)	⬇️
... and 73 more

---

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[codecov]

Codecov Report

Merging #4828 into master will decrease coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4828      +/-   ##
==========================================
- Coverage   95.72%   95.64%   -0.09%     
==========================================
  Files         113      113              
  Lines       25666    25163     -503     
  Branches     2505     2498       -7     
==========================================
- Hits        24570    24068     -502     
+ Misses        773      772       -1     
  Partials      323      323

Flag	Coverage Δ
#linux	95.45% <ø> (-0.09%)	⬇️
#osx	93.29% <ø> (ø)	⬆️
#windows	93.67% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
testing/test_modimport.py	81.81% <0%> (-1.52%)	⬇️
testing/code/test_source.py	95.53% <0%> (-1.07%)	⬇️
testing/test_argcomplete.py	68.11% <0%> (-0.9%)	⬇️
testing/test_compat.py	91.13% <0%> (-0.63%)	⬇️
testing/test_skipping.py	97.65% <0%> (-0.57%)	⬇️
src/_pytest/warnings.py	88.88% <0%> (-0.53%)	⬇️
src/_pytest/debugging.py	77.98% <0%> (-0.41%)	⬇️
src/_pytest/fixtures.py	97.91% <0%> (-0.31%)	⬇️
src/_pytest/logging.py	94.96% <0%> (-0.31%)	⬇️
testing/test_assertrewrite.py	83.55% <0%> (-0.3%)	⬇️
... and 73 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f494eef...d9bdf5c. Read the comment docs.

[nicoddemus]

Thanks @Zac-HD!