Create a Write Data section in the User Guide

[ChucklesOnGitHub]

• Include whatever is right regarding whether to use MatrixWriter or CsvWriter, or whatever new node Bonsai comes up with. Possible text: "For high data rates, use xref:Bonsai.Dsp.MatrixWriter. For lower data rates or files that store human-readable data, use xref:Bonsai.IO.CsvWriter. For videos, use xref:Bonsai.Vision.Writer --> I also think the choice is related to whether the data is buffered or not
• if it depends on the data type, include how to know what type of data a node produces (by either checking the reference or by using the text visualizer or whatever the actual method is).
• include video writers too Add description of ffmpeg video writer  #165