Add messages for Facebook github bot

bots/NewIssueGreeting.md

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+Hey <person>, thanks for reporting this issue!
+
+We've started using a new website called **[Product Pains](https://productpains.com/product/react-native/?tab=top)** to help the community **prioritize issues**.
+
+We have limited bandwidth, it's therefore important to know which issues should be fixed first. The reason Product Pains works better than github is that people can **vote on issues**. On github it's possible to [sort issues by the number of comments](https://github.com/facebook/react-native/issues?q=is%3Aissue+is%3Aopen+sort%3Acomments-desc) but that gives only a very rough estimate.
+
+If you want to help the community prioritize, go ahead and give [Product Pains](https://productpains.com/product/react-native/?tab=top) a try. You can link to this issue from Product Pains.
+
+There are also other ways to get help - see the [README](https://github.com/facebook/react-native#getting-help).

bots/QuestionGreeting.md

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+*By analyzing the title and description for some common words it looks like this issue might be a question. If this is wrong please cc mkonicek.*
+
+Please consider using [Stack Overflow](http://stackoverflow.com/questions/tagged/react-native) for questions. It's the best system for Q&A and the best way to get questions answered.
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+Many people from the community hang out on Stack Overflow and will be able to see your question. If Stack Overflow works for you, consider posting there and closing this issue.

bots/README.md

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+These are the comments inserted by the Facebook github bot to new issues.