fix(tokens): add readme for the @material/web/tokens/versions folder

PiperOrigin-RevId: 836373118

Author: asyncliz

tokens/versions/README.md

@@ -0,0 +1,26 @@
+This folder contains auto-generated files for Material Design token versions.
+
+> **WARNING: These files may unexpectedly change across different non-major
+> versions of `@material/web`.**
+>
+> Most users should ignore this folder and use other APIs provided by
+> `@material/web/tokens`.
+
+`@material/web/tokens/versions` is useful for custom implementations of or
+experimentations with the Material Design system.
+
+To avoid unexpected breakages when using these files, save the *exact version*
+of `@material/web` instead of a version range (e.g. `@2.0.0` instead of
+`@^2.0.0`).
+
+```
+Example of a minor breaking change:
+
+<!-- v2.0.0 - add tokens v5 -->
+@material/[email protected]/tokens/version/v5_0/_md-sys-color.scss
+
+The path to this file may break in a typically non-breaking minor version bump.
+
+<!-- v2.1.0 - update v5 tokens to include a new component -->
+@material/[email protected]/tokens/version/v5_1/_md-sys-color.scss
+```