minor fixes for the Getting Started page

[KS-HTK]

• fixed the python versions named. (contained 3.6 and 3.7)
• fixed the indentation of code examples. There seems to be a bug in the toolchain doing the conversion to html. So a propper fix is near impossible. The best solution was to add explicit code block tags and unindent the content. This shows broken in my Markdown viewer but looks fine in the jekyll dev server. But it is not ideal.
• added python statement to the explicit code blocks where applicable. This adds syntax highlighting to the commands making it easier to read.

closes issue #3