Modified the common starting paragraph of all tutorials to make more sense.

Modified the common starting paragraph of all tutorials to download sandbox.

PREVIOUS SENTENCE
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Download to run this...

MODIFIED VERSION OF THE SAME
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Download the Hortonworks Sandbox to run this...

NEED FOR CHANGE
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The previous sentence does not say what to download.

Does n't it make more sense to do the same change to all non-community tutorials too?