DP: Update getting started section - execution #390
Description
As a visitor to the developer portal, I want to clearly know how to get started solving my problem by using Steem, so that I have a good initial first impression.
Finish the work outlined in #375. Execution is mostly complete.
Supporting
Use https://github.com/steemit/devportal/tree/375-getting-started-page as a base. See bolded todo: notes in intro.md file
Other portions of #389 will need to be completed first. (Urls need to be populated)