Add README for the servo crate (servo#43654)

Add `readme` field to libservo's Cargo.toml, pointing to the repository
root
README via `../../README.md`. This ensures the crates.io page displays
content
when the crate is published, as Cargo copies the referenced file into
the
package during `cargo publish`.

Testing: This change only adds a metadata field to Cargo.toml and does
not
affect build output or runtime behavior. No tests are required.
fixes servo#43143

Signed-off-by: staysafe020 <jambongralpher@gmail.com>

Author: StaySafe020

components/servo/Cargo.toml

@@ -8,6 +8,7 @@ publish.workspace = true
 rust-version.workspace = true
 repository.workspace = true
 description.workspace = true
+readme = "../../README.md"
 
 [lib]
 name = "servo"