[docs] clarify simulate using a different sampling scheme

[odow]

Closes #691

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (1050457) 92.74% compared to head (abc49ca) 92.74%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #692 +/- ## ======================================= Coverage 92.74% 92.74% ======================================= Files 27 27 Lines 3351 3351 ======================================= Hits 3108 3108 Misses 243 243 ```

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[odow]

cc @HenriDeh is this any better:

https://sddp.dev/previews/PR692/guides/simulate_using_a_different_sampling_scheme/

I've added

# Note: `Ω` is defined at the top of this page of documentation

in places

[HenriDeh]

Yes totally. It will help people like me who tunnel-vision save some time :)