Document Android SDK dependency for tests (#797) Tests will fail unless there is an Android SDK available on the system. This PR documents the Android SDK requirement in the "Tests" section of `README.md`. See: https://github.com/bazelbuild/rules_jvm_external/issues/763

diff --git a/README.md b/README.md
index ec5be8d..536bdc0 100644
--- a/README.md
+++ b/README.md

@@ -1136,7 +1136,7 @@
 
 Certain IPv4/IPv6 dual-stack environments may require flags to override the default settings for downloading dependencies, for both Bazel's native downloader and Coursier as a downloader:
 
-Add: 
+Add:
 
 * `startup --host_jvm_args=-Djava.net.preferIPv6Addresses=true` to your `.bazelrc` file for Bazel's native downloader.
 * `-Djava.net.preferIPv6Addresses=true to the `COURSIER_OPTS` environment variable to provide JVM options for Coursier.
@@ -1165,6 +1165,8 @@
 
 ### Tests
 
+In order to run tests, your system must have an Android SDK installed. You can install the Android SDK using [Android Studio](https://developer.android.com/studio), or through most system package managers.
+
 ```
 $ bazel test //...
 ```