Add basic spin linting documentation (pytorch#167227)

This adds basic documentation of the linting features for Spin added in pytorch#167226 to the CONTRIBUTING.md document.

Pull Request resolved: pytorch#167227
Approved by: https://github.com/atalman, https://github.com/albanD

Author: zklaus

CONTRIBUTING.md

@@ -14,6 +14,10 @@ aspects of contributing to PyTorch.
   - [Tips and Debugging](#tips-and-debugging)
 - [Nightly Checkout & Pull](#nightly-checkout--pull)
 - [Codebase structure](#codebase-structure)
+- [Spin](#spin)
+  - [Linting](#linting)
+    - [default lint](#default-lint)
+  - [Regenerating](#regenerating)
 - [Unit testing](#unit-testing)
   - [Python Unit Testing](#python-unit-testing)
   - [Better local unit tests with `pytest`](#better-local-unit-tests-with-pytest)
@@ -274,6 +278,46 @@ dependencies as well as the nightly binaries into the repo directory.
   * ...
 * [.circleci](.circleci) - CircleCI configuration management. [README](.circleci/README.md)
 
+## Spin
+
+[Spin](https://github.com/scientific-python/spin) is a developer cli tool that
+helps running common tasks.
+To list the available tasks, run `spin --help`.
+Currently, we support the following tasks with Spin:
+
+### Linting
+
+Spin helps with linting by making sure that lintrunner is installed correctly
+and by isolating the lintrunner environment from the general development
+environment using uv.
+
+|command||
+|-|-|
+|`setup-lint`|update lintrunner and perform a fresh setup|
+|`lazy-setup-lint`|only perform setup if the lint configuration has changed|
+|`lint`|perform default lint (see below)|
+|`quicklint`|perform lint on all files changed in the latest commit and the working directory|
+|`quickfix`|autofix issues on all files changed in the latest commit and the working directory|
+
+#### default lint
+
+Since some linters take a long time to run, we categorize all linters as either
+fast or slow. In the default lint, only the fast linters are run on all files;
+the slow linters are run on the changed files only.
+
+### Regenerating
+
+Pytorch makes use of a number of code generations, which range from the version
+information in `torch/version.py` over type stubs and other linter support to
+github workflows.
+With Spin, we offer a unified interface to these tasks.
+
+|command||
+|-|-|
+|`regenerate-version`|regenerate `torch/version.py`|
+|`regenerate-type-stubs`|regenerates type stubs for use by static type checkers|
+|`regenerate-clangtidy-files`|regenerates clang related files needed for linting|
+
 ## Unit testing
 
 ### Python Unit Testing