add doc for adding self-hosted runner

docs/08-miscellaneous/tests.md

@@ -20,3 +20,70 @@ We build a test CI system based on Github Actions which will automatically run u
 The test workflow is defined in `.github/workflows/test-ci.yml`.
 
 [//]: # (There's one thing noticeble. We add a Pre-check section before we formally run all the unit tests. The Pre-check section is used to make sure the torch multiprocessing memory sharing and pbt-based environments work as expected. The reason we have this Pre-check is that sometimes the running environment provided by Github Actions is unstable (mostly likely has low limits for memory) and fails our multi-policies and pbt tests.)
+
+### self-hosted runners
+Github Actions supports self-hosted runners for more powerful hardware resources or customized needs. You need to register your runner(physical, virtual, in a container, on-premises, or in a cloud) to Github and define your workflows.
+
+- Step 1: register your runner
+
+  Basically, go to your repository, then go to "Settings", then go to Actions, then go to Runners, then click "New self-hosted runner", then choose the os type and architecture type, then execute the corresponding commands on your runner. You can find concrete steps here: https://docs.github.com/en/actions/hosting-your-own-runners/adding-self-hosted-runners
+
+- Step 2: define your workflows
+
+  Here is an example workflow config for a Google Cloud VM instance(n1-standard-8, Intel Haswell, NVIDIA Tesla P4). 
+
+```yml
+name: tests
+
+on:
+  push:
+    branches:
+    - self-hosted-runner
+
+jobs:
+  run-tests-self-runner:
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ['3.8']
+    runs-on: self-hosted
+    steps:
+    - uses: actions/checkout@v3
+    - name: Create conda env
+      run: |
+        which conda
+        conda env list
+        conda env remove -n self-hosted-runner
+        conda create -n self-hosted-runner python=${{ matrix.python-version }}
+    - name: Add conda to system path
+      run: |
+        echo "/opt/conda/envs/self-hosted-runner/bin" >> $GITHUB_PATH
+    - name: Install dependencies
+      run: |
+        pwd
+        pip install -e '.[atari, mujoco, envpool]'
+        nvcc -V
+        pip install torch==1.9.1+cu111 torchvision==0.10.1+cu111 torchaudio==0.9.1 -f https://download.pytorch.org/whl/torch_stable.html
+        conda list
+    - name: Install test dependencies
+      run: |
+        pip install pytest
+    - name: Run Pre-check
+      uses: nick-fields/retry@v2
+      with:
+        timeout_minutes: 10
+        max_attempts: 5
+        command: pytest -s tests/test_precheck.py & pytest -s tests/algo/test_pbt.py
+    - name: Run tests
+      run: |
+        # run all tests
+        pytest -s -k "not torch_tensor_share"
+```
+
+If you wanna run it for scheduled times, you can change the trigger event to "schedule". For example, the following setting triggers the workflow every day at 5:30 and 17:30 UTC:
+
+```yml
+on:
+  schedule:
+    - cron:  '30 5,17 * * *'
+```