Fix apko-cache link (#1521)

Fixes a link to apko-cache doc in
https://edu.chainguard.dev/open-source/apko/bazel-rules/

Signed-off-by: Garry Ing <[email protected]>

content/open-source/apko/bazel-rules.md

@@ -151,7 +151,7 @@ For more examples checkout the [examples](https://github.com/chainguard-dev/rule
 | <a id="apko_image-architecture"></a>architecture |  the CPU architecture which this image should be built to run on. See https://github.com/chainguard-dev/apko/blob/main/docs/apko_file.md#archs-top-level-element   | String | optional | <code>""</code> |
 | <a id="apko_image-args"></a>args |  additional arguments to provide when running the <code>apko build</code> command.   | List of strings | optional | <code>[]</code> |
 | <a id="apko_image-config"></a>config |  Label to the <code>apko.yaml</code> file.   | <a href="https://bazel.build/concepts/labels">Label</a> | required |  |
-| <a id="apko_image-contents"></a>contents |  Label to the contents repository generated by translate_lock. See [apko-cache](./apko-cache.md) documentation.   | <a href="https://bazel.build/concepts/labels">Label</a> | required |  |
+| <a id="apko_image-contents"></a>contents |  Label to the contents repository generated by translate_lock. See [apko-cache](https://github.com/chainguard-dev/rules_apko/blob/main/docs/apko-cache.md) documentation.   | <a href="https://bazel.build/concepts/labels">Label</a> | required |  |
 | <a id="apko_image-output"></a>output |  -   | String | optional | <code>"oci"</code> |
 | <a id="apko_image-tag"></a>tag |  tag to apply to the resulting docker tarball. only applicable when <code>output</code> is <code>docker</code>   | String | required |  |