docs/manual: add CVS support documentation

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

docs/manual/adding-packages-generic.txt

@@ -266,6 +266,13 @@ information is (assuming the package name is +libfoo+) :
      Buildroot performs a checkout which is preserved as a tarball in
      the download cache; subsequent builds use the tarball instead of
      performing another checkout.
+  ** +cvs+ for retrieving source code from a CVS repository.
+     Used by default when +LIBFOO_SITE+ begins with +cvs://+.
+     The downloaded source code is cached as with the +svn+ method.
+     Only anonymous pserver mode is supported.
+     +LIBFOO_SITE+ 'must' contain the source URL as well as the remote
+     repository directory. The module is the package name.
+     +LIBFOO_VERSION+ is 'mandatory' and 'must' be a timestamp.
   ** +git+ for retrieving source code from a Git repository.  Used by
      default when +LIBFOO_SITE+ begins with +git://+. The downloaded
      source code is cached as with the +svn+

docs/manual/prerequisite.txt

@@ -52,7 +52,7 @@ Optional packages
 +
 In the official tree, most of the package sources are retrieved
 using +wget+; a few are only available through their +git+, +mercurial+,
-or +svn+ repository.
++svn+ or +cvs+ repository.
 +
 All other source fetching methods are implemented and may be used in a
 development context (further details: refer to xref:download-infra[]).