meson: install the man pages for the command line tools

https://bugzilla.gnome.org/show_bug.cgi?id=796274
diff --git a/tools/meson.build b/tools/meson.build
index 98757eb..57595fb 100644
--- a/tools/meson.build
+++ b/tools/meson.build
@@ -7,6 +7,7 @@
   include_directories: [configinc],
   dependencies : tool_deps,
 )
+install_man('gst-device-monitor-@0@.1'.format(api_version))
 
 executable('gst-discoverer-@0@'.format(api_version),
   'gst-discoverer.c',
@@ -15,6 +16,7 @@
   include_directories: [configinc],
   dependencies : tool_deps,
 )
+install_man('gst-discoverer-@0@.1'.format(api_version))
 
 executable('gst-play-@0@'.format(api_version),
   'gst-play.c', 'gst-play-kb.c',
@@ -23,3 +25,4 @@
   include_directories: [configinc],
   dependencies : tool_deps + [libm],
 )
+install_man('gst-play-@0@.1'.format(api_version))