Doc: Improve readme (#130)

* Add context

* Update README.md

* Update README.md

Co-authored-by: greged93 <82421016+greged93@users.noreply.github.com>

* Update README.md

Co-authored-by: greged93 <82421016+greged93@users.noreply.github.com>

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Co-authored-by: greged93 <82421016+greged93@users.noreply.github.com>

README.md

@@ -2,6 +2,12 @@
 
 This repository contains the execution of the EF standard execution layer tests.
 
+The Ethereum Foundation provides a suite of [official tests](https://github.com/ethereum/tests) to verify the compliance of EVM clients.
+Passing all these tests qualifies allows a client to gain confidence on his execution layer.
+For further information, please refer to the [official documentation](https://ethereum-tests.readthedocs.io/en/latest/).
+
+Kakarot is an EVM running within CairoVM, coupled with a [RPC](https://github.com/kkrt-labs/kakarot-rpc/tree/main), which would make it possible to run these tests using the Ethereum Foundation runner ([retesteth](https://github.com/ethereum/retesteth)). However, in order to limit the possible number of interactions and avoid adding failing points, we develop our own simplified test runner based on Reth's ef-tests runner.
+
 ## Requirements
 
 - nextest: to install [nextest](https://nexte.st/index.html), run `cargo install cargo-nextest --locked`