Have serai-runtime compile again

substrate/runtime/README.md

@@ -0,0 +1,14 @@
+# Serai Runtime
+
+The on-chain rules for the Serai blockchain.
+
+### Compilation
+
+If compilation fails due to `borsh`, this is likely due to attempting to
+compile to WASM binary (`no-std`) while `borsh` believes it's being compiled in
+a `std` context. Serai uses a patched [`substrate-wasm-builder`](
+  https://github.com/serai-dex/serai/tree/develop/polkadot-sdk/substrate/utils/wasm-builder
+) which clears the `CARGO_FEATURE_STD` environment variable to prevent this,
+yet `target/` directories may be contaminated if a build ever occurs without
+the patched `substrate-wasm-builder`. Please attempt a clean build to resolve
+the error.