dev-manual: Review edits to the package installation section

Fixes [YOCTO #9672]

A couple typos here needed fixed.  Also, a missing statement in
the JSON example.

(From yocto-docs rev: 8756cb363a70a8b77077a666c62c0f678ffb3d3e)

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

documentation/dev-manual/dev-manual-common-tasks.xml

@@ -9401,7 +9401,7 @@
                 A JSON file is used to define the packages needed by a test.
                 This file must be in the same path as the file used to define
                 the tests.
-                Furthermore, the filename must map directory to the test
+                Furthermore, the filename must map directly to the test
                 module name with a <filename>.json</filename> extension.
             </para>
 
@@ -9434,7 +9434,7 @@
                 DUT.
                 <literallayout class='monospaced'>
      {
-         "": {
+         "foo": {
              "pkg": "bar"
          },
          "foobar": [