Modified the description for the property 'prefix'.
add ability to pass in app path for sd app deployed to  manhattan
Added example for using HB helpers.
Made some edits.
Made changes based on Caridy's feedback.
Merge pull request #1018 from lzhan/testnum

add ability to pass in app path for sd app deployed to  manhattan
Merge pull request #1019 from zhouyaoji/docs_hb_helpers

[doc] Created documentation how to use and create Handlebars helpers. The documentation also includes an example and overview of the Helpers addon.