Update creating_a_strategy.md
Update creating_a_strategy.md

Adding new and simple strategy example to help users to understand how to build their own strategies.
Also, we're describing the candle variables so user can know what to read when building strategies.

I haven't described the "candle.vwp" variable since I don't really know what it is.
pprados/gekko,pprados/gekko,BarnumD/gekko,generalectric/gekko,generalectric/gekko,nourchawich/gekko,askmike/gekko,nourchawich/gekko,BarnumD/gekko,pprados/gekko,BarnumD/gekko,nourchawich/gekko,WXLWEB/gekko,WXLWEB/gekko,askmike/gekko,generalectric/gekko,WXLWEB/gekko,askmike/gekko