message: added explanatory comment
  Explains why libsodium is done over URL
diff: # Setup Indy SDK build environment for MacOS
  1. Install Rust and rustup (https://www.rust-lang.org/install.html).
  -2. Install required native libraries and utilities
  +2. Install required native libraries and utilities (libsodium is added with URL since non-latest version is required for it to function)
  ```
  brew install pkg-config
  brew install cmake
  brew install openssl
  ```
  +
  +
  3. Setup environment variables:
  ```
  export PKG_CONFIG_ALLOW_CROSS=1
  