Add docblock to torch/_dynamo/trace_rules.py (pytorch#155401)

Add comprehensive module docstring explaining the tracing rules and policies
that govern TorchDynamo's compilation decisions, including skip rules,
inlining policies, and library-specific handling.

Originally generated by claude but reviewed and edited by me.

Pull Request resolved: pytorch#155401
Approved by: https://github.com/williamwen42

Author: bobrenjc93

torch/_dynamo/trace_rules.py

@@ -1,4 +1,26 @@
 # mypy: allow-untyped-defs
+
+"""
+Tracing rules and policies for TorchDynamo compilation decisions.
+
+This module defines the rules that govern what code TorchDynamo should trace and compile
+versus what should be executed eagerly. It contains functions and classes that determine:
+
+- Which modules, functions, and objects should be skipped during tracing
+- Which parts of the code should cause graph breaks
+- How to handle different Python libraries and third-party packages
+- Rules for determining when to inline functions vs calling them eagerly
+
+Key components:
+- Skip rules: Functions that return True if an object should be skipped during tracing
+- Inlining rules: Policies for when to inline function calls during compilation
+- Library-specific handling: Special cases for popular Python packages
+- Performance heuristics: Rules that balance compilation overhead vs runtime benefits
+
+These rules are critical for TorchDynamo's ability to automatically determine
+compilation boundaries and optimize PyTorch programs effectively.
+"""
+
 import abc
 import builtins
 import collections