docs(ref): Finish a sentence on rust-versions (#14884)

### What does this PR try to resolve?

Was about to point someone to the docs when I found this

### How should we test and review this PR?

### Additional information

Author: weihanglo

src/doc/src/reference/rust-version.md

@@ -86,7 +86,7 @@ What Rust versions to support is a trade off between
 Users of your package are most likely to track their supported Rust versions to:
 - Their Rust toolchain vendor's support policy, e.g. The Rust Project or a Linux distribution
   - Note: the Rust Project only offers bug fixes and security updates for the latest version.
-- A fixed schedule for users to re-verify their packages with the new toolchain, e.g. the first release of the year, every 
+- A fixed schedule for users to re-verify their packages with the new toolchain, e.g. the first release of the year, every 5 releases.
 
 In addition, users are unlikely to be using the new Rust version immediately but need time to notice and re-verify or might not be aligned on the exact same schedule..