docs: add documentation for benchmarks

closes #5312

benchmarks/README.md

@@ -0,0 +1,34 @@
+# Express Benchmarks
+
+## Installation
+
+You will need to install [wrk](https://github.com/wg/wrk/blob/master/INSTALL) in order to run the benchmarks.
+
+## Running
+
+To run the benchmarks, first install the dependencies `npm i`, then run `make`
+
+The output will look something like this:
+
+```
+  50 connections
+  1 middleware
+ 7.15ms
+ 6784.01
+
+ [...redacted...]
+
+  1000 connections
+  10 middleware
+ 139.21ms
+ 6155.19
+
+```
+
+### Tip: Include Node.js version in output
+
+You can use `make && node -v` to include the node.js version in the output.
+
+### Tip: Save the results to a file
+
+You can use `make > results.log` to save the results to a file `results.log`.