Compile Click-specific guidelines

Reformat whole file to 80 characters limit
Refs: https://github.com/pallets/click/pull/3239/changes#r3058361631

Author: kdeldycke

docs/contributing.md

@@ -1,21 +1,44 @@
 # Contributing
 
-This is a quick reference for Click-specific development tasks. For setting up the development environment and the general contribution workflow, see the Pallets [quick reference](https://palletsprojects.com/contributing/quick/) and the [detailed contributing guide](https://palletsprojects.com/contributing/).
+This is a quick reference for Click-specific development
+tasks. For setting up the development environment and the
+general contribution workflow, see the Pallets [quick
+reference](https://palletsprojects.com/contributing/quick/)
+and the [detailed contributing
+guide](https://palletsprojects.com/contributing/).
 
 ## Extra Test Environments
 
 Click includes some extra test environments:
 
--   `tox r -e stress` runs stress tests for race conditions in Click's test runner.
+-   `tox r -e stress` runs stress tests for race conditions
+    in Click's test runner.
 
     ```shell-session
     $ tox r -e stress
     ```
 
--   `tox r -e random` runs tests in parallel in a random order to detect test pollution.
+-   `tox r -e random` runs tests in parallel in a random
+    order to detect test pollution.
 
     ```shell-session
     $ tox r -e random
     ```
 
--   A CI workflow (`.github/workflows/test-flask.yaml`) runs Flask's test suite to catch downstream regressions.
+-   A CI workflow (`.github/workflows/test-flask.yaml`)
+    runs Flask's test suite to catch downstream
+    regressions.
+
+## Code Style
+
+Avoid ternary expressions (`x if cond else y`): coverage
+cannot measure both branches. Use an explicit `if`/`else`
+block instead.
+
+Do not add unnecessary dependencies. If a feature can be
+implemented with the standard library, do not pull in an
+external package for it.
+
+## Formatting
+
+Wrap lines in Markdown files at 80 characters.