Update rust.md

[DrewRidley]

Made documentation a bit more clear on how cargo component works

[itowlson]

I think this might cause cascading changes further down (e.g. line 74). Could you say a bit more about the unclearness you ran into and/or how this would have helped you? Thanks!

[vados-cosmonic]

Hey thanks for this suggestion @DrewRidley -- since I just added some changes related to the Rust code, I incorporated these changes here over in #222 so hopefully they're a bit clearer!

@itowlson please feel free to take a look there as well if you can find the time -- The guide should still read well, and I tried to maintain consistency. Many of the places where we mentioned add (as the project name/in a folder), should generally say adder now. The rust code actually never had a file called add.rs or anything like that, but I believe there were one or two places where we referenced the WIT dir (i.e. adder/wit).

[kate-goldenring]

@DrewRidley thank you for pointing out how to make this more consistent. @vados-cosmonic pulled this change in with his PR, so I am going to close this one.