I Installed forge on http://files.minecraftforge.net/ like you said above, when I ran the .jar as an administration. Then I told it to install the client. Finally, it asked if I wanted to allow it to make changes to my device and I said yes so that it would complete. I used Twitch to open the minecraft launcher because I wanted to play RLcraft.
Here's the screen shot of what the launcher looks like when I pressed the button in Twitch which said 'play' underneath the RLcraft picture: