Adds zpool split to man page

Adds zpool split documentation to the zpool man page.  I only documented
the options that I could get to work.   While it is documented on some
sun blogs that devices can be specified for split, I was not able to get
that to work during my testing.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1456

man/man8/zpool.8

@@ -137,6 +137,11 @@ zpool \- configures ZFS storage pools
 \fBzpool set\fR \fIproperty\fR=\fIvalue\fR \fIpool\fR
 .fi
 
+.LP
+.nf
+\fBzpool split\fR [\fB-n\fR] [\fB-R\fR \fIaltroot\fR] [\fB-o\fR \fIproperty=value\fR] \fIpool\fR \fInewpool\fR
+.fi
+
 .LP
 .nf
 \fBzpool status\fR [\fB-xv\fR] [\fIpool\fR] ...
@@ -1600,6 +1605,51 @@ Stop scrubbing.
 Sets the given property on the specified pool. See the "Properties" section for more information on what properties can be set and acceptable values.
 .RE
 
+.sp
+.ne 2
+.mk
+.na
+\fBzpool split\fR [\fB-n\fR] [\fB-R\fR \fIaltroot\fR] [\fB-o\fR \fIproperty=value\fR] \fIpool\fR \fInewpool\fR
+.ad
+.sp .6
+.RS 4n
+Split devices off \fIpool\fR creating \fInewpool\fR.  All \fBvdev\fRs in \fIpool\fR must be mirrors.  At the time of the split, \fInewpool\fR will be a replica of \fIpool\fR.
+
+.sp
+.ne 2
+.mk
+.na
+\fB\fB-n\fR \fR
+.ad
+.sp .6
+.RS 4n
+Do dry run, do not actually perform the split. Print out the expected configuration of \fInewpool\fR.
+.RE
+
+.sp
+.ne 2
+.mk
+.na
+\fB\fB-R\fR \fIaltroot\fR \fR
+.ad
+.sp .6
+.RS 4n
+Set \fIaltroot\fR for \fInewpool\fR and automaticaly import it.  This can be useful to avoid mountpoint collisions if \fInewpool\fR is imported on the same filesystem as \fIpool\fR.
+.RE
+
+.sp
+.ne 2
+.mk
+.na
+\fB\fB-o\fR \fIproperty=value\fR \fR
+.ad
+.sp .6
+.RS 4n
+Sets the specified property for \fInewpool\fR. See the “Properties” section for more information on the available pool properties.
+.RE
+
+.RE
+
 .sp
 .ne 2
 .mk