readme: Add section about precompiles support

README.md

@@ -89,6 +89,20 @@ To build the evmone EVMC module (shared library), test, and benchmark:
    build/bin/evmone-bench test/evm-benchmarks/benchmarks
    ```
 
+### Precompiles
+
+Ethereum Precompiled Contracts (_precompiles_ for short) are not directly supported by evmone.
+
+However, there are options to enable limited precompiles support for testing.
+
+1. The [test/state/precompiles_stub.json](./test/state/precompiles_stub.json) contains
+   precompiles execution results for inputs commonly used in tests.
+   You can use the precompiles STUB by setting the environment variable
+   `EVMONE_PRECOMPILES_STUB=./test/state/precompiles_stub.json`.
+2. The CMake option `EVMONE_PRECOMPILES_SILKPRE=1` enables building of
+   the [silkpre] third party library with the implementation of the precompiles.
+   This library also requires [GMP] (e.g. libgmp-dev) library for building and execution.
+
 ### Tools
 
 #### evm-test
@@ -138,10 +152,12 @@ Licensed under the [Apache License, Version 2.0].
 [EVMC]: https://github.com/ethereum/evmc
 [Ipsilon]: https://github.com/ipsilon
 [Ewasm]: https://github.com/ewasm
+[GMP]: https://gmplib.org
 [intx]: https://github.com/chfast/intx
 [ethash]: https://github.com/chfast/ethash
 [Releases]: https://github.com/ethereum/evmone/releases
 [standard readme]: https://github.com/RichardLitt/standard-readme
+[silkpre]: https://github.com/torquem-ch/silkpre
 
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