ref-manual: Added detail to the populate_sysroot task.

Provided more detail in the first sentence.

Fixes [YOCTO #9968]

(From yocto-docs rev: 15080a565bafdfffe0c13a0a18fd1c011773cc25)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/ref-tasks.xml

@@ -423,7 +423,9 @@
         <para>
             Copies a subset of the files installed by the
             <link linkend='ref-tasks-install'><filename>do_install</filename></link>
-            task into the sysroot to make them available to other recipes.
+            task into the sysroot directory
+            <filename>${STAGING_DIR_HOST}</filename> to make
+            them available to other recipes.
             Files that would typically not be needed by other recipes at build
             time are skipped.
             Skipped files include files installed into