Fix typo and add rust version info to contributing guide [ci skip]
@@ -54,8 +54,11 @@ Thank you! We'll try to get back to you as soon as possible.
1. Install Rust using [rustup], which allows you to easily switch between Rust
versions.
+
+ Diesel currently supports Rust Stable, Nightly, Rust Beta.
+
2. Install the system libraries needed to interface with the database systems
- you which to use.
+ you wish to use.
These are the same as when compiling diesel. In general, it is a good idea
to have _all_ drivers installed so you can run all tests locally.
