Create FAQ.md

Fixes: #11

FAQ.md

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+# About the preview service
+
+## How do I add a skin to the preview service?
+
+[Create a new issue](https://github.com/jdlrobson/skins.wmflabs.org/issues/new?assignees=&labels=&projects=&template=enable-preview-for-my-skin-on-https---skins-demo-wmflabs-org-.md&title=Please+enable+my+skin+for+live+preview+option)
+
+## How often does the preview get updated?
+
+Every new MediaWiki release, I will pull the latest code for your skin. If your skin fatals I will disable it and file an issue against your skin. I will also update the entry on MediaWiki.org to mark it as **unstable**.
+
+## My skin's preview got disabled! How do I restore it?
+
+First make sure your skin is no longer fataling and the fixes are merged into master/main branch. Please also address any deprecation warnings before requesting an update.
+
+Then please 
+[Create a new issue](https://github.com/jdlrobson/skins.wmflabs.org/issues/new?assignees=&labels=&projects=&template=enable-preview-for-my-skin-on-https---skins-demo-wmflabs-org-.md&title=Please+enable+my+skin+for+live+preview+option) to get the skin restored on the demo service.