Include README.md in published crate

[burgerdev]

Relative paths work correctly:

$ cargo publish --dry-run
[...]
$ tar tzf target/package/glome-0.3.0.crate
glome-0.3.0/.cargo_vcs_info.json
glome-0.3.0/Cargo.lock
glome-0.3.0/Cargo.toml
glome-0.3.0/Cargo.toml.orig
glome-0.3.0/README.md
glome-0.3.0/src/cli/bin.rs
glome-0.3.0/src/dalek.rs
glome-0.3.0/src/lib.rs
glome-0.3.0/src/openssl.rs