docs: Add contributing guide and docs about performance tests (#235)

.github/CONTRIBUTING.md

@@ -0,0 +1,81 @@
+# Notes for contributors
+
+1. Python hooks are supported now too. All you have to do is:
+    1. add a line to the `console_scripts` array in `entry_points` in `setup.py`
+    2. Put your python script in the `pre_commit_hooks` folder
+
+Enjoy the clean, valid, and documented code!
+
+* [Run and debug hooks locally](#run-and-debug-hooks-locally)
+* [Run hook performance test](#run-hook-performance-test)
+  * [Run via BASH](#run-via-bash)
+  * [Run via Docker](#run-via-docker)
+  * [Check results](#check-results)
+  * [Cleanup](#cleanup)
+
+## Run and debug hooks locally
+
+```bash
+pre-commit try-repo {-a} /path/to/local/pre-commit-terraform/repo {hook_name}
+```
+
+I.e.
+
+```bash
+pre-commit try-repo /mnt/c/Users/tf/pre-commit-terraform terraform_fmt # Run only `terraform_fmt` check
+pre-commit try-repo -a ~/pre-commit-terraform # run all existing checks from repo
+```
+
+Running `pre-commit` with `try-repo` ignores all arguments specified in `.pre-commit-config.yaml`.
+
+## Run hook performance test
+
+To check is your improvement not violate performance, we have dummy execution time tests.
+
+Script accept next options:
+
+| #   | Name                               | Example value                                                            | Description                                          |
+| --- | ---------------------------------- | ------------------------------------------------------------------------ | ---------------------------------------------------- |
+| 1   | `TEST_NUM`                         | `200`                                                                   | How many times need repeat test                      |
+| 2   | `TEST_COMMAND`                     | `'pre-commit try-repo -a /tmp/159/pre-commit-terraform terraform_tfsec'` | Valid pre-commit command                             |
+| 3   | `TEST_DIR`                         | `'/tmp/infrastructure'`                                                  | Dir on what you run tests.                           |
+| 4   | `TEST_DESCRIPTION`                 | ```'`terraform_tfsec` PR #123:'```                                       | Text that you'd like to see in result                |
+| 5   | `RAW_TEST_`<br>`RESULTS_FILE_NAME` | `terraform_tfsec_pr123`                                                  | (Temporary) File where all test data will be stored. |
+
+### Run via BASH
+
+```bash
+# Install deps
+sudo apt install -y datamash
+# Run tests
+./hooks_performance_test.sh 200 'pre-commit try-repo -a /tmp/159/pre-commit-terraform terraform_tfsec' '/tmp/infrastructure' '`terraform_tfsec` v1.51.0:' 'terraform_tfsec_pr159'
+```
+
+### Run via Docker
+
+```bash
+# Build `pre-commit` image
+docker build -t pre-commit --build-arg INSTALL_ALL=true .
+# Build test image
+docker build -t pre-commit-tests tests/
+# Run
+TEST_NUM=1
+TEST_DIR='/tmp/infrastructure'
+PRE_COMMIT_DIR="$(pwd)"
+TEST_COMMAND='pre-commit try-repo -a /pct terraform_tfsec'
+TEST_DESCRIPTION='`terraform_tfsec` v1.51.0:'
+RAW_TEST_RESULTS_FILE_NAME='terraform_tfsec_pr159'
+
+docker run -v "$PRE_COMMIT_DIR:/pct:rw" -v "$TEST_DIR:/lint:ro" pre-commit-tests \
+    $TEST_NUM "$TEST_COMMAND" '/lint' "$RAW_TEST_RESULTS_FILE_NAME" "$RAW_TEST_RESULTS_FILE_NAME"
+```
+
+### Check results
+
+Results will be located at `./test/results` dir.
+
+### Cleanup
+
+```bash
+sudo rm -rf tests/results
+```