fixup: docs.rs builds

Cargo.toml

@@ -64,3 +64,9 @@ tempfile = "3.3.0"
 strip = true  # Automatically strip symbols from the binary.
 opt-level = "z"  # Optimize for size.
 lto = true
+
+[package.metadata.docs.rs]
+# NOTE(cole-h): We embed the Nix closure by reading from this environment variable, but this is not
+# available in docs.rs's build. It doesn't influence docs, so it's fine to set it to a bogus (but
+# existing-file) value.
+cargo-args = ["--config", "env.NIX_INSTALLER_TARBALL_PATH=\"../Cargo.toml\""]