Add rule ID for variadic function syntax

We're missing a rule identifier above the description of the syntax
for variadic functions.  Let's add that.
1 file changed
tree: bd0ccc3b871f3454044ac963086bb3fd685b4542
  1. .cargo/
  2. .github/
  3. dev-guide/
  4. docs/
  5. src/
  6. theme/
  7. tools/
  8. .gitattributes
  9. .gitignore
  10. book.toml
  11. Cargo.lock
  12. Cargo.toml
  13. CONTRIBUTING.md
  14. LICENSE-APACHE
  15. LICENSE-MIT
  16. README.md
  17. reference.md
  18. rust-toolchain.toml
  19. rustfmt.toml
  20. triagebot.toml
README.md

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