generate_gradle.py: Allow multiple --target and add --all

docs/android_studio.md

Index: docs/android_studio.md
diff --git a/docs/android_studio.md b/docs/android_studio.md
index 96ef1752ef52997d61c39137f34ae368f94d3984..35690bc55c4e81c543f446f996e9736bb22e7791 100644
--- a/docs/android_studio.md
+++ b/docs/android_studio.md
@@ -5,10 +5,21 @@
 ## Usage
 
 ```shell
-build/android/gradle/generate_gradle.py --output-directory out-gn/Debug --target //chrome/android:chrome_public_test_apk
+build/android/gradle/generate_gradle.py --output-directory out-gn/Debug
 ```
 
-This creates a project at `out-gn/Debug/gradle`. To create elsewhere: `--project-dir foo`
+This creates a project at `out-gn/Debug/gradle`. To create elsewhere:
+
+```shell
+build/android/gradle/generate_gradle.py --output-directory out-gn/Debug --project-dir my-project
+```
+
+By default, only common targets are generated. To customize the list of targets
+to generate projects for:
+
+```shell
+build/android/gradle/generate_gradle.py --output-directory out-gn/Debug --target //some:target_apk --target //some/other:target_apk
+```
 
 For first-time Android Studio users: