Add proper documentation for secrets file

Author: Chris Dawson

chapter-7-android-and-git-data/README.md

@@ -25,3 +25,24 @@ ANDROID_HOME=~/Android/Sdk \
 
 This single test proves that our GitHub client Java code makes a new file inside the Jekyll repository
 and then views the published post.
+
+To run the espresso test, you will need to create a `secrets.xml` file inside `app/src/main/res/values`.
+This file should contain the same username and password and look like this:
+
+```
+<?xml version="1.0" encoding="utf-8"?>
+<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
+    <string name="github_helper_username">BurningOnUp</string>
+    <string name="github_helper_password">somethingOrOther</string>
+</resources>
+```
+
+Then, to run the tests, use this command:
+
+```
+GITHUB_HELPER_USERNAME=BurningOnUp \
+GITHUB_HELPER_PASSWORD=somethingOrOther \
+JAVA_HOME=~/bin/jdk1.7.0_79 \
+ANDROID_HOME=~/Android/Sdk \
+./gradlew connectedTest
+```