Add initial page for important myst syntax.

[MFraters]

This add a page to the developer documentation on the important syntax for writing documentation in issue #532.

I think it is almost done, but I may need to add a few more syntax elements.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d465a69) 93.49% compared to head (bb40640) 93.54%.
Report is 27 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #542      +/-   ##
==========================================
+ Coverage   93.49%   93.54%   +0.05%     
==========================================
  Files          92       92              
  Lines        6346     6340       -6     
==========================================
- Hits         5933     5931       -2     
+ Misses        413      409       -4     

see 1 file with indirect coverage changes

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[github-actions]

Benchmark	Main	Feature	Difference (99.9% CI)
Slab interpolation simple none	1.023 ± 0.004 (s=460)	1.024 ± 0.005 (s=422)	-0.0% .. +0.1%
Slab interpolation curved simple none	1.026 ± 0.003 (s=481)	1.025 ± 0.003 (s=399)	-0.1% .. +0.0%
Spherical slab interpolation simple none	1.259 ± 0.005 (s=360)	1.258 ± 0.003 (s=358)	-0.1% .. +0.0%
Slab interpolation simple curved CMS	1.054 ± 0.011 (s=426)	1.054 ± 0.011 (s=430)	-0.3% .. +0.2%
Spherical slab interpolation simple CMS	1.862 ± 0.007 (s=251)	1.860 ± 0.005 (s=235)	-0.2% .. +0.0%
Spherical fault interpolation simple none	1.272 ± 0.004 (s=354)	1.271 ± 0.005 (s=356)	-0.1% .. +0.0%
Cartesian min max surface	2.361 ± 0.017 (s=191)	2.363 ± 0.020 (s=193)	-0.2% .. +0.4%
Spherical min max surface	7.358 ± 0.016 (s=55)	7.352 ± 0.018 (s=70)	-0.2% .. +0.1%

[gassmoeller]

Just a few small comments. Fix them then this is good to go.

[gassmoeller]

missing newline at end of file

[gassmoeller]

this format is different from your current format. Want to update?