404 Links in Exercises 0 and 7

[zediogoviana]

Hey 👋 It seems that some links in Exercises 0 and 7 are pointing to some 404 pages.

Exercise 0:

• https://docs.substrate.io/fundamentals/runtime-development/
• https://docs.substrate.io/fundamentals/runtime-development/#composing-a-runtime-with-pallets
• https://docs.substrate.io/fundamentals/runtime-development/#frame
• https://docs.substrate.io/tutorials/work-with-pallets/custom-pallet/

Exercise 7:

• https://docs.rs/frame-support/latest/frame_support/traits/trait.Imbalance.html
• https://docs.rs/frame-support/latest/frame_support/traits/trait.Currency.html