Adding subsection on address and contract types (#4479)

## Description
Closes #2704

## Checklist

- [x] I have linked to any relevant issues.
- [x] I have commented my code, particularly in hard-to-understand
areas.
- [x] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [ ] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

---------

Co-authored-by: Kin Chan <calldelegation@calldelegation.local>

docs/book/src/reference/solidity_differences.md

@@ -25,3 +25,7 @@ Math in the FuelVM is by default safe (i.e. any overflow or exception is a panic
 ## No* Code Size Limit
 
 There is no practical code size limit to Sway contracts. The physical limit is governed by the [`VM_MAX_RAM` VM parameter](https://fuellabs.github.io/fuel-specs/master/vm#parameters), which at the time of writing is 64 MiB.
+
+## Account Types
+
+Account types in the FuelVM have type-safe wrappers around primitive `b256` hashes to clearly distinguish their respective types. The wrapper `Address` mirrors that of an EOA (Externally Owned Account) and has the ability to hold UTXOs in the context of the EVM. The other wrapper, `ContractId`, reflects that of a deployed contract in the EVM but cannot hold UTXOs.