update readme - nightly no longer required

README.md

@@ -15,9 +15,8 @@ In this tutorial, we will create a brand new index with the articles of English
 
 There are a couple ways to install `tantivy-cli`.
 
-If you are a Rust programmer, you probably have `cargo` and `rustup` installed and you can just
-run `rustup run nightly cargo install tantivy-cli`. (`cargo install tantivy-cli` will work
-as well if nightly is your default toolchain).
+If you are a Rust programmer, you probably have `cargo` installed and you can just
+run `cargo install tantivy-cli`
 
 Alternatively, you can directly download a
 static binary for [Linux x86 64](https://github.com/tantivy-search/tantivy-cli/releases/download/0.4.2/tantivy-cli-0.4.2-x86_64-unknown-linux-musl.tar.gz) or for [Mac OS X](https://github.com/tantivy-search/tantivy-cli/releases/download/0.4.2/tantivy-cli-0.4.2-x86_64-apple-darwin.tar.gz)