Document reliable App Store export path

apple/AppStore/DISTRIBUTION.md

@@ -52,6 +52,7 @@ cargo run -p ironstorage-apple-release -- verify .
 5. Export and upload with the checked-in App Store Connect export options:
 
    ```sh
+   PATH=/usr/bin:/bin:/usr/sbin:/sbin:/Applications/Xcode.app/Contents/Developer/usr/bin \
    xcodebuild -exportArchive \
      -archivePath /private/tmp/IronStorage.xcarchive \
      -exportPath /private/tmp/IronStorage-AppStore \
@@ -59,6 +60,10 @@ cargo run -p ironstorage-apple-release -- verify .
      -allowProvisioningUpdates
    ```
 
+   Keep this restricted `PATH`: Xcode's system `rsync` otherwise starts a
+   Homebrew `rsync` server, which interprets `-E` differently and fails with
+   `exportArchive Copy failed` and `--extended-attributes: unknown option`.
+
 6. In App Store Connect, complete the listing from `metadata.toml`, upload the
    reviewed required-size iPhone screenshots and Watch screenshots, answer
    privacy and encryption questions, provide