Describe the usage for benchmarks

Author: isidentical

extras/profiling/README.md

@@ -6,8 +6,25 @@ to automate this testing accross versions.
 
 ## Usage
 
-### Requirements
-
+Ensure the following requirements are satisfied:
 - Python 3.7+
 - `pyperf`
 
+Then, run the `extras/benchmarks/run.py`:
+```
+$ python extras/profiling/run.py
+```
+
+Without any options, this command will initially create
+an isolated environment and install `httpie` from the
+latest commit. Then it will create a second environment
+with the `master` of the current repository and run the
+benchmarks on both of them. It will compare the results
+and print it as a markdown table:
+
+| Benchmark                              | master | this_branch          |
+|----------------------------------------|:------:|:--------------------:|
+| `http --version` (startup)             | 201 ms | 174 ms: 1.16x faster |
+| `http --offline pie.dev/get` (startup) | 200 ms | 174 ms: 1.15x faster |
+| Geometric mean                         | (ref)  | 1.10x faster         |
+