servo: Merge #4099 - Add .cargo/config to .gitignore, move content to ports/android (from SimonSapin:cargo-config); r=mbrubeck

This allows using `.cargo/config` at the root of the repository for local path override, without risk of accidentally committing it.

However I don’t have the environment to test the Android build. Would this break it?

Source-Repo: https://github.com/servo/servo
Source-Revision: b5d6864de1000d6d54c2d5ebfd90ea9f6a596c54

--HG--
rename : servo/.cargo/config => servo/ports/android/.cargo/config

servo/.gitignore

@@ -1,3 +1,4 @@
+/.cargo/config
 /target
 /rust
 /cargo