fix(l2): add missing requirements to run the L2 (#2512)

**Motivation**

Build fails if requirements are not met. In particular, solc versions
need to be the requirements

**Description**

This adds a short description of the requirements

---------

Co-authored-by: Martin Paulucci <martin.c.paulucci@gmail.com>

Author: MauroToscano

crates/l2/docs/README.md

@@ -13,9 +13,17 @@ For more detailed documentation on each part of the system:
 - [Prover](./prover.md)
 - [State Diffs](./state_diffs.md)
 - [Withdrawals](./withdrawals.md)
+  
+## Prerequisites
 
+- [Rust](https://www.rust-lang.org/tools/install)
+- [Solc 0.29](https://docs.soliditylang.org/en/latest/installing-solidity.html)
+- [Docker](https://docs.docker.com/engine/install/)
+  
 ## Quick HandsOn
 
+Make sure docker is running!
+
 1. `cd crates/l2`
 2. `make rm-db-l2 && make down`
    - It will remove any old database, if present, stored in your computer. The absolute path of libmdbx is defined by [data_dir](https://docs.rs/dirs/latest/dirs/fn.data_dir.html).