[benchmark] StringDistance: Increase ASCII workload

benchmark/single-source/StringDistance.swift

@@ -112,6 +112,23 @@ let asciiString = #"""
   high-level constructs like objects, protocols, closures, and generics. Swift
   embraces modules, eliminating the need for headers and the code duplication
   they entail.
+
+  Swift toolchains are created using the script
+  [build-toolchain](https://github.com/apple/swift/blob/main/utils/build-toolchain).
+  This script is used by swift.org's CI to produce snapshots and can allow for
+  one to locally reproduce such builds for development or distribution purposes.
+  A typical invocation looks like the following:
+
+  ```
+    $ ./swift/utils/build-toolchain $BUNDLE_PREFIX
+  ```
+
+  where ``$BUNDLE_PREFIX`` is a string that will be prepended to the build date
+  to give the bundle identifier of the toolchain's ``Info.plist``. For instance,
+  if ``$BUNDLE_PREFIX`` was ``com.example``, the toolchain produced will have
+  the bundle identifier ``com.example.YYYYMMDD``. It will be created in the
+  directory you run the script with a filename of the form:
+  ``swift-LOCAL-YYYY-MM-DD-a-osx.tar.gz``.
   """#
 
 let asciiRanges = (