Create FAQ.md

FAQ.md

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+# Frequently asked questions
+
+### 1. The app downloads the update but it won't install the update?
+
+<img src="/images/gif/update-failed-install.gif" width="180">
+
+This happen when the app that you are testing in-app updates is **not signed with the same signing key** as the one available from 
+Google Play.The reason is android OS is not able to install the update as the app that you are testing is not signed.(ie using the debug 
+version)
+#### Fix
+
+Generate a signed apk using the same signing key(key used to sign the app uploaded to Google Play) and install it in your device. This will 
+download and install the update.
+
+Generate a signed apk            |  Use the same signing key
+:-------------------------:|:-------------------------:
+<img src="/images/step2.jpg" width="250">  |  <img src="/images/step3.jpg" width="250">