Document that compressed archive of a folder can be downloaded

add examples specifying version using
- a ref
- a commit id

Change-Id: I9a519f4674ecbf0a4b632e240cd203a1150d4770

Documentation/api-reference.md

diff --git a/Documentation/api-reference.md b/Documentation/api-reference.md
index 0dab3c0..99ee0ee 100644
--- a/Documentation/api-reference.md
+++ b/Documentation/api-reference.md
@@ -46,6 +46,13 @@
 Supported formats: `.tar.gz` and `.zip`
 ```bash
 curl "https://gerrit.googlesource.com/a/gitiles/+archive/refs/heads/master.tar.gz" -o repo.tar.gz
+curl "https://gerrit.googlesource.com/a/gitiles/+archive/30851aacbea3370c7be8179c890b3401526242eb.tar.gz" -o repo.tar.gz
+```
+
+Download a compressed archive of a folder `java/com/google/gitiles/dev/` in a repository at a specific commit or ref.
+```bash
+curl "https://gerrit.googlesource.com/a/gitiles/+/refs/heads/master/java/com/google/gitiles/dev.tar.gz" -o dev.tar.gz
+curl "https://gerrit.googlesource.com/a/gitiles/+/30851aacbea3370c7be8179c890b3401526242eb/java/com/google/gitiles/dev.tar.gz" -o dev.tar.gz
 ```
 
 #### **`+doc`**