gerrit: how to use download-gerrit-topic.py

Change-Id: Iedd340789632e2f986ebaecbe3596337cfe48f85

GettingStarted.md

diff --git a/GettingStarted.md b/GettingStarted.md
index b8e8b7e..8913598 100644
--- a/GettingStarted.md
+++ b/GettingStarted.md
@@ -155,6 +155,19 @@
 repo upload -t --re ${REVIEWER} --cc ${CC_LIST} # To upload the change to Gerrit for review
 ```
 
+### How to download CLs of a Gerrit topic?
+
+If you are reviewing a bunch of CLs from different projects, that are grouped
+under a single topic in Gerrit, you can download the latest CL of each project
+(replace `TOPIC` with the topic you are reviewing):
+
+```bash
+download-gerrit-topic.py TOPIC
+```
+
+By default, the new branches under which the CLs will be downloaded are named
+`TOPIC`. See `download-gerrit-topic.py --help` for more details.
+
 ### Help! I'm on a limited-bandwidth connection, and need to stop downloading tooling!
 
 There's an environment variable you can set called `PIN_TOOLCHAINS` to prevent