Update subsections "Receiving inputs" and "Constructing a Gamepad" of Gamepad Interface for touch inputs.

[bradleyneedham]

Section "Partial Gamepad Interface" is missing subsections "Receiving inputs" and "Constructing a Gamepad" as it relates to inputs from a touch surface.
In the main spec the subsections describe the steps followed when "the system receives new button or axis input values".
This spec should provide the same information for when the system receives touch input values.

I have already made the changes and can submit a PR, however to follow the process I believe that this issue should be created first and approved.

@sagoston and @fernando-80 requested I make these changes.

[sagoston]

Approved, please create a PR.