Add global gitignore setup instructions
PiperOrigin-RevId: 454911808
Change-Id: If1c88a6291974abc41946e41ca0131731c756860
diff --git a/docs/onboarding.md b/docs/onboarding.md
index aeff486..666cb08 100644
--- a/docs/onboarding.md
+++ b/docs/onboarding.md
@@ -138,7 +138,17 @@
git config --global diff.renameLimit 999999
```
-### To check out older source, use the superproject
+### Set up Git file exclusions {#source-exclude}
+
+Mac users should consider adding `.DS_Store` to a global `.gitignore` file to
+avoid accidentally checking in local metadata files:
+
+```shell
+echo .DS_Store>>~/.gitignore
+git config --global core.excludesFile '~/.gitignore'
+```
+
+### To check out older sources, use the superproject {#source-historical}
The
[git superproject](https://android.googlesource.com/platform/superproject/+/androidx-main)
