docs: restore accidentally lost code block info string

I accidentally lost it in b125bec9914bd211d77719bd60bc5a23bd9db579.
(I should have changed the info string to ```rust ignore.)

1 files changed, 1 insertions, 1 deletions

diff --git a/README.md b/README.md
index a1f8a82..5da2675 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ Spec-compliant HTML parsing [requires both tokenization and tree-construction][p
 While this crate implements a spec-compliant HTML tokenizer it does not implement any
 tree-construction. Instead it just provides a `NaiveParser` that may be used as follows:
 
-```
+```rust
 use std::fmt::Write;
 use html5tokenizer::{NaiveParser, Token};