fix typos, PACKAGE -> PACKAGES

doc/fai-guide.txt

@@ -1096,7 +1096,7 @@ install the software, so this archive is downloaded to the directory
 the file shouldn't be removed, use the command _PRELOAD_ instead.
 
 It's possible to append a list of class names after the command for
-apt-get. So this _PACKAGE_ command will only be executed when at least
+apt-get. So this _PACKAGES_ command will only be executed when at least
 one of the corresponding classes is defined (logical OR). So you can
 combine many small files
 into the file DEFAULT. WARNING! Use this feature only in the file
@@ -1115,8 +1115,8 @@ removed automatically from the installation list only if the command _install_ i
 The concept of classes priority allows a higher priority class (one
 that comes later in the sequence of classes) to override the selection
 of packages of a lower priority class.  For this to work correctly,
-the higher priority class must use the same _PACKAGE_ command (e.g.
-_PACKAGE install-norec_ instead of just _PACKAGE install_) as the one
+the higher priority class must use the same _PACKAGES_ command (e.g.
+_PACKAGES install-norec_ instead of just _PACKAGES install_) as the one
 used by the class it is trying to override.  This is useful to suppress
 installation of a package, for example, to avoid installing the 'linuxlogo'
 package installed by class FAIBASE:
@@ -1844,7 +1844,7 @@ squash image is served from.
 
 You can install all sorts of Linux distributions from a single Debian
 nfsroot. Therefore you have to create a base.tar.xz of the distribution
-you like to install and place it info the `basefiles` directory. Then
+you like to install and place it into the `basefiles` directory. Then
 name it UBUNTU1404.tar.xz for example. An install client which belongs
 to the class UBUNTU1404 then extracts this base file into its empty
 file system. Additionally you have to adjust the 'sources.list' or