Add README.md to be published on NPM

Fixes #154

Signed-off-by: Bernd Hufmann <Bernd.Hufmann@ericsson.com>

timeline-chart/README.md

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+## Description
+
+A time graph / gantt chart library for large data (e.g. traces).
+
+## Additional Information
+
+- [Documentation](https://github.com/theia-ide/timeline-chart/blob/master/doc/documentation.md): Detailed description of the timeline-chart library and its components.
+- [Theia Trace Extension](https://github.com/theia-ide/theia-trace-extension): A reference application that uses the timeline-chart library.
+
+## Screenshots
+
+![timeline-chart](https://raw.githubusercontent.com/theia-ide/timeline-chart/master/doc/images/screenshot1-0.0.1.png)
+![timeline-chart](https://raw.githubusercontent.com/theia-ide/timeline-chart/master/doc/images/screenshot2-0.0.1.png)
+