rustc.1: Fix sysroot documentation.

Author: Elly Jones

man/rustc.1

@@ -78,7 +78,8 @@ object file to \fBfoo.o\fR.
 .TP
 \fB--time-llvm-passes\fR: Print runtimes of llvm phases.
 .TP
-\fB--sysroot\fR \fIpath\fR: Set the system root. Default is rustc's directory.
+\fB--sysroot\fR \fIpath\fR: Set the system root. Default is the directory above
+rustc's.
 .TP
 \fB--target\fR \fIgnu-config-name\fR: Set the compilation target, which is a
 string of the form \fBcpu\fR-\fBmanufacturer\fR-\fBkernel\fR[-\fBos\fR]. Example