WIP: Updates Advanced/Transcode/Add a logo

Hello @Garf. This updates the documentation from the wiki https://wiki.videolan.org/VLC_HowTo/Add_a_logo/ mentioned in #7 (and also using the video-filter as mentioned in https://wiki.videolan.org/Documentation:Modules/logo/). As the options mentioned in the "logo video-filer" module can be used to adjust the settings with the other two methods as well, I have mentioned the options globally for all three methods, along with adding a GUI method.

About the troubleshooting part mentioned in https://wiki.videolan.org/VLC_HowTo/Add_a_logo/, I checked the logs and found that VLC is using Bicubic for handling the scaling, so I wanted to confirm if pixelation (or change in aspect ratio of the logo) can still occur. If it is still possible, I will add the section in this documentation.

I have also left out "Dynamically change logo using RC" for the time being, as I could not implement it. I will ask on the IRC to check if the syntax mentioned in the wiki is still valid.