adt-manual: Fixed PMS typo

Fixes [YOCTO #8419]

There was a typo in the section that indicated the file extensions
for various Package Management Systems.  The one for RPM used a
file extension of ".rms".  I fixed it to ".rpm".

(From yocto-docs rev: 7b303a789d4f11aed6ebc83d734a27442a531b52)

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

documentation/adt-manual/adt-package.xml

@@ -27,7 +27,7 @@
                 information about OPKG.</para></listitem>
             <listitem><para><emphasis>RPM:</emphasis> A more widely known PMS intended for GNU/Linux
                 distributions.
-                This PMS works with files packaged in an <filename>.rms</filename> format.
+                This PMS works with files packaged in an <filename>.rpm</filename> format.
                 The build system currently installs through this PMS by default.
                 See <ulink url='http://en.wikipedia.org/wiki/RPM_Package_Manager'></ulink>
                 for more information about RPM.</para></listitem>