Code Review: Add model.md

[AgustinVallejo]

For #88

[jonathanolson]

Assign me once this is done for review (I'll also be available to help create it, if so that won't be needed)

[samreid]

@AgustinVallejo said this is ready for review. @jonathanolson can you please take a look?

[AgustinVallejo]

I believe this, along #97 are ready for review

[jonathanolson]

I think it would be good to put the Lab mode configurations into the model.md, so that people can see what coordinates they start with (without being rounded at all). Since we're setting them in "model" units, they would be getting rounded "view" units.

[jonathanolson]

Oops, actually, they're referenced! We'll need to not break that link.

[jonathanolson]

Made some changes above, can you review?

Additionally, I think it would be good to mention some things about collisions. Does it preserve momentum?

[jonathanolson]

Looks good, just the one item above!

[AgustinVallejo]

Added a big section with Physical Simplifications, to adress body sizes, mass scales, collisions, and how accurate is each pre-set with their real world counterparts. So another fast review would be nice.

[jonathanolson]

This is excellent!

My only question would be whether the "Distances and Sizes" and "Radii of Bodies" are really separate - they are both talking about the radii/size (same thing?), and might be combinable.

[AgustinVallejo]

I think they work good separately, because one section is stating that body sizes are actually way bigger than in reality, the other one states that we are using a particular mapping function between mass and radii. Closing.