Add direct links to documentation

Make the URL to the documentation of each of the library crates known so
that it will be easier to click through to it from a crates.io search.

Signed-off-by: Daniel Müller <deso@posteo.net>

Author: d-e-s-o

libbpf-cargo/Cargo.toml

@@ -6,6 +6,7 @@ rust-version.workspace = true
 repository.workspace = true
 homepage.workspace = true
 license.workspace = true
+documentation = "https://docs.rs/libbpf-cargo"
 description = "Cargo plugin to build bpf programs"
 readme = "README.md"
 authors = ["Daniel Xu <dxu@dxuuu.xyz>", "Daniel Müller <deso@posteo.net>"]

libbpf-rs/Cargo.toml

@@ -6,6 +6,7 @@ rust-version.workspace = true
 repository.workspace = true
 homepage.workspace = true
 license.workspace = true
+documentation = "https://docs.rs/libbpf-rs"
 description = "libbpf-rs is a safe, idiomatic, and opinionated wrapper around libbpf-sys"
 readme = "README.md"
 authors = ["Daniel Xu <dxu@dxuuu.xyz>", "Daniel Müller <deso@posteo.net>"]