Update README.md

Installing SBEToolbox
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1. After you download SBEToolbox, extract and change into that directory.
2. See help install which shows what directory paths will be prepended to MATLAB path
3. Run install function which will add appropriate paths to MATLAB path and opens pathtool
4. Now click on "Save" to save the paths and then on "Close" to close pathtool window.
5. SBEToolbox is now installed.
6. To start the UI, just type "SBEGUI" at the prompt.