chore: Link to actual MSRV Fx is using (#1836)

Instead of having to look it up in a table.

Cargo.toml

@@ -19,7 +19,7 @@ version = "0.7.5"
 edition = "2021"
 license = "MIT OR Apache-2.0"
 # Don't increase beyond what Firefox is currently using:
-# https://firefox-source-docs.mozilla.org/writing-rust-code/update-policy.html#schedule
+# https://searchfox.org/mozilla-central/search?q=MINIMUM_RUST_VERSION&path=python/mozboot/mozboot/util.py
 rust-version = "1.74.0"
 
 [workspace.dependencies]