add dummy type fields for pkgbuild generators

This field is required in order to pass config validation in case if
section name differs from default one. Also by default keyring_generator
and mirrorlist_generator have been renamed to keyring-generator and
mirrorlist-generator respectively for consistence

docs/faq.rst

@@ -767,7 +767,7 @@ The application provides special plugin which generates keyring package. This pl
    .. code-block:: ini
 
       [keyring]
-      target = keyring_generator
+      target = keyring-generator
 
    By default it will use ``sign.key`` as trusted key and all other keys as packagers ones. For all available options refer to :doc:`configuration <configuration>`.
 
@@ -802,12 +802,12 @@ The application provides special plugin which generates mirrorlist package also.
    .. code-block:: ini
 
       [mirrorlist]
-      target = mirrorlist_generator
+      target = mirrorlist-generator
 
-      [mirrorlist_generator]
+      [mirrorlist-generator]
       servers = https://repo.example.com/$arch
 
-   The ``mirrorlist_generator.servers`` must contain list of available mirrors, the ``$arch`` and ``$repo`` variables are supported. For more options kindly refer to :doc:`configuration <configuration>`.
+   The ``mirrorlist-generator.servers`` must contain list of available mirrors, the ``$arch`` and ``$repo`` variables are supported. For more options kindly refer to :doc:`configuration <configuration>`.
 
 #.
    Create package source files: