add treeless clones to GitHub Actions guidance

README.md

@@ -383,12 +383,13 @@ By default, [GitHub Actions](https://github.com/features/actions/), [Azure Pipel
 
 To build in GitHub Actions, Azure Pipelines, or Travis CI, configure them to fetch a sufficient number of commits.
 
-For GitHub Actions, set the `fetch-depth` of the [checkout action](https://github.com/actions/checkout) to an appropriate number, or to zero for all commits. For example:
+For GitHub Actions, set the `fetch-depth` of the [checkout action](https://github.com/actions/checkout) to an appropriate number, or to zero for all commits (you can also set `filter` to `tree:0` to create a [treeless clone](https://github.blog/2020-12-21-get-up-to-speed-with-partial-clone-and-shallow-clone/), for better performance). For example:
 
 ```yaml
 - uses: actions/checkout@v2
   with:
     fetch-depth: 0
+    filter: tree:0
 ```
 
 For Azure Pipelines, include an explicit [checkout step](https://learn.microsoft.com/en-us/azure/devops/pipelines/yaml-schema/steps-checkout) and set the `fetchDepth` to an appropriate number, or to zero for all commits: