add note for check orientation (#211)

docs/source/documentation/brainreg/user-guide/checking-orientation.md

@@ -16,3 +16,9 @@ Top is the reference atlas, averaged for all directions and bottom is the aligne
 ## Correct orientation
 Top is the reference atlas, averaged for all directions and bottom is the aligned input data with correct input
 ![correct-orientation](../images/correct_orientation.png)
+
+## A note about the camera position
+
+In asymmetric cases (e.g. if you are registering to a single hemisphere or an asymmetric atlas), you may wonder about the camera position you are viewing the projections from. The origin of the projection image is at its top-left corner, the first axis runs top-down, and the second axis runs from left to right. 
+
+For example, if the atlas is ASR, projection 1 (along the S-I axis) will have the anterior-most, right-most (AR) point on the top-left, with the A-P axis running from the top to the bottom of the screen, and the R-L axis running from left to right. This means you are viewing the brain from "below" (from inferior to superior).