docs: add version pinning information to the README

This should provide an easy reference for users starting to use this
action who want to pin versions, so that they can easily identify the
different versioning pattern used by this action.

Signed-off-by: Justin Chadwell <me@jedevc.com>

README.md

@@ -20,6 +20,7 @@ ___
 
 * [Usage](#usage)
 * [Configuring your builder](#configuring-your-builder)
+* [Version pinning](#version-pinning)
 * [Customizing](#customizing)
   * [inputs](#inputs)
   * [outputs](#outputs)
@@ -58,6 +59,33 @@ jobs:
 
 See https://docs.docker.com/build/ci/github-actions/configure-builder/
 
+## Version pinning
+
+This action builds images using [Buildx](https://github.com/docker/buildx) and
+[BuildKit](https://github.com/moby/buildkit). By default, the action will
+attempt to use the latest version of Buildx available on the GitHub Runner
+(the build client) and the latest release of BuildKit (the build server).
+
+To pin to a specific version of Buildx, use the `version` input. For example,
+to pin to Buildx v0.10.0:
+
+```yaml
+- name: Set up Docker Buildx
+  uses: docker/setup-buildx-action@v3
+  with:
+    version: v0.10.0
+```
+
+To pin to a specific version of BuildKit, use the `image` option in the
+`driver-opts` input. For example, to pin to BuildKit v0.11.0:
+
+```yaml
+- name: Set up Docker Buildx
+  uses: docker/setup-buildx-action@v3
+  with:
+    driver-opts: image=moby/buildkit:v0.11.0
+```
+
 ## Customizing
 
 ### inputs