Update explain_postscript.rst_

Author: PaulWessel

doc/rst/source/explain_postscript.rst_

@@ -4,8 +4,9 @@ Note on PostScript
 If the user selects **ps** as one of the formats, then please be aware that
 it is recommended you first set the desired paper size.  With **ps**\ , GMT needs to
 work with a fixed paper size since, unlike the **eps** format, there will be
-no cropping to BoundingBox.  If no paper size is specified via :term:`PS_MEDIA`
+no cropping to a tight BoundingBox.  If no paper size is specified via :term:`PS_MEDIA`
 then GMT will default to A4 and issue a warning; GMT is unable to determine if that
 size is adequate for your plot but if the canvas width exceeds A4 paper width we will
-switch page orientation to landscape. For all other formats the final dimension will
+switch page orientation to landscape. Note that any other graphics formats specified
+with **ps** will also not be cropped.  Otherwise, for all other formats the final dimension will
 be determined automatically.