Document reversed polarity

[isaacplotkin]

Users are confused why the raw EEG data has reversed polarity. We should explain why this happens and that they should reverse polarity in preprocessing if needed.

The reversed polarity was a conscious decision that allows us to design an ExG bio-sensing system since each channel can be individually configured. Here is a forum post that goes into more detail https://openbci.com/forum/index.php?p=/discussion/2042/polarity-of-erp-signal

[retiutut]

Relates to data saved from the OpenBCI GUI. Though, we can also save data in BrainFlow CSV and BDF format.

Resolving this issue also means specifying if this is true for all data sent from the board, or just from the GUI.

^^^ This would determine which doc(s) to put the info.