Add more content to the README [ci skip]

Ref #9.

Author: Preetam

README.md

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 # explain-analyzer [![CircleCI](https://circleci.com/gh/Preetam/explain-analyzer.svg?style=svg)](https://circleci.com/gh/Preetam/explain-analyzer)
+
+This is a web-based MySQL explain analyzer.
+
+You can use it here: https://preetam.github.io/explain-analyzer/#!/explain/
+
+### Features
+
+* Table representation of MySQL JSON explain output
+* Comments about explain interpretation
+* Experimental scalability analysis
+* Explain saving and permalinks
+
+### Screenshot
+
+<img src="https://user-images.githubusercontent.com/379404/34457844-21dc9180-ed8c-11e7-8e70-270e391b971e.png" width=422/>
+
+### License
+
+BSD 2-Clause (see [LICENSE](LICENSE))