Update readme

README.md

@@ -20,3 +20,93 @@
 ```shell
 pip install pytest-codspeed
 ```
+
+## Usage
+
+### Creating benchmarks
+
+Creating benchmarks with `pytest-codspeed` is compatible with the standard `pytest-benchmark` API. So if you already have benchmarks written with it, you can start using `pytest-codspeed` right away.
+
+#### Marking a whole test function as a benchmark with `pytest.mark.benchmark`
+
+```python
+import pytest
+from statistics import median
+
+@pytest.mark.benchmark
+def test_median_performance():
+    return median([1, 2, 3, 4, 5])
+```
+
+#### Benchmarking selected lines of a test function with the `benchmark` fixture
+
+```python
+import pytest
+from statistics import mean
+
+def test_mean_performance(benchmark):
+    # Precompute some data useful for the benchmark but that should not be
+    # included in the benchmark time
+    data = [1, 2, 3, 4, 5]
+
+    # Benchmark the execution of the function
+    benchmark(lambda: mean(data))
+
+
+def test_mean_and_median_performance(benchmark):
+    # Precompute some data useful for the benchmark but that should not be
+    # included in the benchmark time
+    data = [1, 2, 3, 4, 5]
+
+    # Benchmark the execution of the function:
+    # The `@benchmark` decorator will automatically call the function and
+    # measure its execution
+    @benchmark
+    def bench():
+        mean(data)
+        median(data)
+```
+
+### Running benchmarks
+
+#### Testing the benchmarks locally
+
+If you want to run only the benchmarks tests locally, you can use the `--codspeed` pytest flag:
+
+```shell
+pytest tests/ --codspeed
+```
+
+> **Note:** Running `pytest-codspeed` locally will not produce any performance reporting. It's only useful for making sure that your benchmarks are working as expected. If you want to get performance reporting, you should run the benchmarks in the CI.
+
+#### In the CI
+
+You can use the [CodSpeedHQ/action](https://github.com/CodSpeedHQ/action) to run the benchmarks in Github Actions and upload the results to CodSpeed.
+
+Example workflow:
+
+```yaml
+name: benchmarks
+
+on:
+  push:
+    branches:
+      - "main" # or "master"
+  pull_request:
+
+jobs:
+  benchmarks:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v3
+        with:
+          python-version: "3.9"
+      - name: Install dependencies
+        run: pip install -r requirements.txt
+      - name: Run benchmarks
+        uses: CodSpeedHQ/action@v1
+        with:
+          token: ${{ secrets.CODSPEED_TOKEN }}
+          run: pytest tests/ --codspeed
+```