OpenVR: Add note about how to enable interactions

For the interaction to work in the OpenVR examples, it is required to copy the action/manifest .json files to the working directory. This adds an according note to the description of these examples

mentioned in commit 489268e1

merged

@codeling thanks for your contribution. All merged now, I had to resolve a few merge conflicts. Also added a blank line to the end of the *.md files and emphasised .json