Add link to benchmarks in documentation (#6257)

docs/reference/benchmarks.md

@@ -0,0 +1,7 @@
+# Benchmarks
+
+uv's performance is continually benchmarked against previous releases, and regularly compared to
+other tools in the space, like pip and Poetry.
+
+The latest benchmarks and details on the benchmarking process can be found in the
+[GitHub repository](https://github.com/astral-sh/uv/blob/main/BENCHMARKS.md).