plan9.ini(8) was lacking documentation for the tiltscreen option, so i wrote some. i based it off of how the others were written.

diff 0e66f87316e571f7edf5274369ec69a5905507aa uncommitted
--- a/sys/man/8/plan9.ini
+++ b/sys/man/8/plan9.ini
@@ -977,6 +977,15 @@
 .BR off .
 The first two specify differing levels of power saving;
 the third turns the monitor off completely.
+.SS \fL*tiltscreen=\fIvalue\fP
+This is used to orient the screen on startup.
+Values are
+.BR left ,
+.BR right ,
+.BR inverted ,
+and
+.BR none .
+If no value is given, the default is none.
 .SS NVRAM
 .SS \fLnvram=\fIfile\fP
 .SS \fLnvrlen=\fIlength\fP