Merge pull request #503 from xwvvvvwx/update-install-instructions

Update install instructions to use rls-preview

Author: nrc

README.md

@@ -59,7 +59,7 @@ rustup update nightly
 Once you have rustup installed, run the following commands:
 
 ```
-rustup component add rls --toolchain nightly
+rustup component add rls-preview --toolchain nightly
 rustup component add rust-analysis --toolchain nightly
 rustup component add rust-src --toolchain nightly
 ```