Add feature for wasm targets (MystenLabs#849)

* Add feature for wasm targets

* Update readme

Author: jonas-lj

Cargo.lock

@@ -73,6 +73,10 @@ $ cargo build --bin ecvrf-cli
 $ target/debug/ecvrf-cli -h
 ```
 
+## WASM
+
+The `fastcrypto` crate can be used when building WASM modules. To do this, enable the `wasm` feature flag when including the `fastcrypto` crate in your `Cargo.toml` file and follow the instructions found in the [Rust and WASM book](https://rustwasm.github.io/docs/book/) to build the WASM module.
+
 ## Tests
 
 There exist unit tests for all primitives in all three crates, which can be run by: 

README.md

@@ -53,6 +53,7 @@ fastcrypto-derive = { path = "../fastcrypto-derive", version = "0.1.3" }
 serde_json = "1.0.93"
 num-bigint = "0.4.4"
 bech32 = "0.9.1"
+getrandom = {version = "0.2.15", features = ["js"], optional = true}
 
 # Required for bulletproofs
 bulletproofs = { version = "4.0.0", optional = true }
@@ -114,6 +115,9 @@ experimental = ["dep:bulletproofs", "dep:merlin"]
 # Include AES and its modes.
 aes = ["dep:aes", "dep:cbc", "dep:aes-gcm", "dep:ctr", "dep:aes-gcm-siv"]
 
+# Needs to be enabled for wasm targets.
+wasm = ["dep:getrandom"]
+
 [dev-dependencies]
 criterion = "0.5.1"
 k256 = { version = "0.11.6", features = ["ecdsa", "sha256", "keccak256"] }