chore: update benchmark information (#316)

Author: ematipico

src/docs/guide/benchmarks.md

@@ -9,6 +9,8 @@ outline: deep
 
 Oxc's parser is at least 3x faster than swc and 5x faster than Biome.
 
+Please note that it is not an apple-to-apple comparison with Biome. Biome's parser [produces a CST](https://biomejs.dev/internals/architecture) instead of an AST, which requires a lot more work.
+
 See repository [bench-javascript-parser-written-in-rust](https://github.com/oxc-project/bench-javascript-parser-written-in-rust).
 
 ## Transformer