testing: instructions in fuzz/README.md don't work: cargo install afl fails

[xpe]

From fuzz/README.md:

# Fuzz Testing

This is the fuzz testing target for the `crc32fast` crate.

1. Install `afl` via `cargo install afl`
2. Build the fuzz target via `cargo afl build`
3. Generate a random input file via `head -c 1000 </dev/urandom >in/random`
3. Run the fuzz test via `cargo afl fuzz -i in -o out -- ./target/debug/fuzz`

But on my system, cargo install afl fails with this error:

error: there is nothing to install in `afl v0.15.10`, because it has no binaries
`cargo install` is only for installing programs, and can't be used with libraries.
To use a library crate, add it as a dependency to a Cargo project with `cargo add`.