Add instruction how to install bindgen

Signed-off-by: Jonathan Schwender <[email protected]>

Readme.md

@@ -25,6 +25,8 @@ Please also check the following:
 - Be sure to guard the new component behind a cargo feature and document the feature in Cargo.toml.
 - If you did not generate the bindings with API-level 10, specify which API-level you generated the bindings with
   and guard the generated module behind the corresponding api-level feature flag.
+- Installing `bindgen`: We use a version of bindgen that has not been released yet to crates.io.
+  You can install the latest version by running `cargo install --git https://github.com/rust-lang/rust-bindgen.git bindgen-cli --branch main --features prettyplease`
 
 ## License