Add additional meta data to improve crate experience

* Add readme setting, so README.md is shown on https://crates.io/
* Add repository setting, so a link to the project repository
  is shown on https://crates.io/

Author: Nicoretti

Cargo.toml

@@ -3,8 +3,12 @@ authors = [
     "Jonathan Pallant <[email protected]>",
     "Jorge Aparicio <[email protected]>",
 ]
+
 description = "A heap allocator for Cortex-M processors"
+repository = "https://github.com/rust-embedded/alloc-cortex-m"
 documentation = "https://docs.rs/alloc-cortex-m"
+readme = "README.md"
+
 keywords = [
     "allocator",
     "arm",