Adds missing preposition to copy and missing labels on two steps in the Issue Board index.html.haml

The missing preposition is just grammar, but labeling steps 6 and 7 as 'steps' rather than 'features' may be debatable, as new lines 207-208 and 238-239 do.

Those changes are to make earlier copy and formatting logically and visually consistent. Previously, the subheader text on line 70 refers to 'step 6' as a step and with a link; when the reader follows the link, step 6 is not labelled as a step, thus these changes. In the code steps 6 and 7 are both called 'steps'. An alternative to adding step-number text for steps 6 and 7 is to change line 70 to refer to step 6 as a 'feature'.