improve wording avoiding bad linebreaks

lksh.1

@@ -1,4 +1,4 @@
-.\" $MirOS: src/bin/mksh/lksh.1,v 1.21 2017/02/18 02:33:13 tg Exp $
+.\" $MirOS: src/bin/mksh/lksh.1,v 1.22 2017/02/27 16:04:37 tg Exp $
 .\"-
 .\" Copyright (c) 2008, 2009, 2010, 2012, 2013, 2015, 2016, 2017
 .\"	mirabilos <m@mirbsd.org>
@@ -74,7 +74,7 @@
 .\" with -mandoc, it might implement .Mx itself, but we want to
 .\" use our own definition. And .Dd must come *first*, always.
 .\"
-.Dd $Mdocdate: February 18 2017 $
+.Dd $Mdocdate: February 27 2017 $
 .\"
 .\" Check which macro package we use, and do other -mdoc setup.
 .\"
@@ -184,17 +184,17 @@ instead.
 .Pp
 Note that it's strongly recommended to invoke
 .Nm
-with at least the
+with
 .Fl o Ic posix
-option, if not both that
-.Em and Fl o Ic sh ,
 to fully enjoy better compatibility to the
 .Tn POSIX
 standard (which is probably why you use
 .Nm
 over
 .Nm mksh
-in the first place) or legacy scripts, respectively.
+in the first place);
+.Fl o Ic sh
+(possibly additionally to the above) may be needed for some legacy scripts.
 .Sh LEGACY MODE
 .Nm
 currently has the following differences from