doc: make setup version independent

I'm not fiddling with this every time I do a release, and it is annoying
for PRs getting filed to do this after every release. Moreover, the
instructions with an old version are still correct, and you'll still get
the latest version of `csv` in a fresh project.

Closes #306

Author: BurntSushi

src/lib.rs

@@ -42,20 +42,12 @@ position information, configuration knobs or iterator types.
 
 # Setup
 
-Add this to your `Cargo.toml`:
-
-```toml
-[dependencies]
-csv = "1.1"
-```
+Run `cargo add csv` to add the latest version of the `csv` crate to your
+Cargo.toml.
 
 If you want to use Serde's custom derive functionality on your custom structs,
-then add this to your `[dependencies]` section of `Cargo.toml`:
-
-```toml
-[dependencies]
-serde = { version = "1", features = ["derive"] }
-```
+then run `cargo add serde --features derive` to add the `serde` crate with its
+`derive` feature enabled to your `Cargo.toml`.
 
 # Example