Fix SDK version mismatch in oxide-sdk README

[niklabh]

Description

The oxide-sdk/README.md tells users to add oxide-sdk = "0.1" to their Cargo.toml, but the actual crate version in oxide-sdk/Cargo.toml is 0.2.1. New developers copying the README snippet will get the wrong version.

What to fix

• Update the version string in oxide-sdk/README.md to match the current version in oxide-sdk/Cargo.toml
• Consider using a placeholder like oxide-sdk = "0.2" or linking to crates.io instead of hard-coding a version

Files involved

• oxide-sdk/README.md
• oxide-sdk/Cargo.toml (reference only)

Difficulty

Beginner — single-line documentation fix. Great for your first contribution!