fix(derive): readme k256 fall-through docs

crates/derive/README.md

@@ -15,7 +15,12 @@ Some features include the following.
 - `k256`: [secp256k1][k] public key recovery support.
 - `online`: Exposes an [alloy-provider][ap] powered data source using "online" HTTP requests.
 
-By default, `kona-derive` enables features `serde` and `k256`. 
+By default, `kona-derive` enables features `serde` and `k256`.
+
+Key recovery using the [secp256k1][k] curve sits behind a `k256` feature flag so that when compiled in `offline` mode,
+secp recovery can fall through to the fpp host, accelerating key recovery. This was necessary since invalid instructions
+were found when compiling `k256` recovery down to a bare-metal MIPS target. Since public key recovery requires elliptic
+curve pairings, `k256` fall-through host recovery should drastically accelerate derivation on the FPVM.
 
 [k]: https://en.bitcoin.it/wiki/Secp256k1 
 [ap]: https://docs.rs/crate/alloy-providers/latest