Add main module header comment

Co-authored-by: ishaan-berri <ishaan-berri@users.noreply.github.com>

litellm/main.py

@@ -1,3 +1,5 @@
+# LiteLLM main module: public completion, embedding, streaming, and moderation entrypoints.
+#
 # +-----------------------------------------------+
 # |                                               |
 # |           Give Feedback / Get Help            |

tests/test_litellm/test_main_module_header.py

@@ -0,0 +1,13 @@
+from pathlib import Path
+
+
+def test_main_py_starts_with_brief_file_description():
+    repo_root = Path(__file__).resolve().parents[2]
+    main_py = repo_root / "litellm" / "main.py"
+
+    first_two_lines = main_py.read_text(encoding="utf-8").splitlines()[:2]
+
+    assert any(
+        "LiteLLM main module" in line and "entrypoints" in line
+        for line in first_two_lines
+    )