Is documentation outdated?

[oslfmt]

I'm basically running the code given in the first example code block of the documentation, just trying to generate a key pair. However, when running the code I get this error:

```error[E0599]: no function or associated item named new found for struct `OsRng` in the current scope
--> src/main.rs:7:26
|
7 | let mut rng = OsRng::new().expect("OsRng");
| ^^^ function or associated item not found in `OsRng`

Furthermore, I've included the rand feature in Cargo.toml:

secp256k1 = { version = "0.21.2", features = ["rand"] }

[tcharding]

You need to enable feature rand-std which enables the rand dependency with std which is needed for OsRng (and also thread_rng).

Which means the example is wrong since it uses rand only. I'll fix it, thanks for pointing this out.