docs: add -h parameter description to xenstore-* man pages

The "-h" parameter is missing in the man pages of the xenstore-*
programs.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

docs/man/xenstore-chmod.1.pod

@@ -42,6 +42,10 @@ write, and set permissions).
 
 =over
 
+=item B<-h>
+
+Show the usage information for xenstore-chmod and exit the program.
+
 =item B<-r>
 
 Apply the permissions to the key and all its I<children>.

docs/man/xenstore-ls.1.pod

@@ -13,6 +13,10 @@ using a nested, tree-like view.
 
 =over
 
+=item B<-h>
+
+Show the usage information for xenstore-ls and exit the program.
+
 =item B<-f>
 
 Show the full path for all keys.

docs/man/xenstore-read.1.pod

@@ -12,6 +12,10 @@ Read values of one or more Xenstore I<PATH>s.
 
 =over
 
+=item B<-h>
+
+Show the usage information for xenstore-read and exit the program.
+
 =item B<-p>
 
 Prefix value with key name.

docs/man/xenstore-write.1.pod

@@ -13,6 +13,10 @@ provided to write them at once - in one Xenstore transaction.
 
 =over
 
+=item B<-h>
+
+Show the usage information for xenstore-write and exit the program.
+
 =item B<-R>
 
 Write raw value, skip parsing escaped characters (\x..).