[C#] how to init for ETH

ffi/cs/readme.md

@@ -8,8 +8,17 @@ cd mcl
 mklib dll
 ```
 
-Open `ffi/cs/mcl.sln` and Set the directory of `mcl/bin` to `workingDirectory` at `Debug` of test project.
+Open `mcl/ffi/cs/mcl.sln` and Set the directory of `mcl/bin` to `workingDirectory` at `Debug` of test project.
 
 # Remark
 - `bn256.cs` is an old code. It will be removed in the future.
-- `mcl/mcl.cs` is a new version. It support `BN254`, `BN_SNARK` and `BLS12_381` curve, which requires `mclbn384_256.dll`.
+- `mcl/mcl.cs` is a new version. It support `BN254`, `BN_SNARK` and `BLS12_381` curve, which requires `mclbn384_256.dll`.
+
+# `ETHmode` with `BLS12_381`
+
+If you need the map-to-G1/G2 function defined in [Hashing to Elliptic Curves](https://www.ietf.org/id/draft-irtf-cfrg-hash-to-curve-09.html),
+then initialize this library as the followings:
+```
+MCL.Init(BLS12_381);
+MCL.ETHmode();
+```