swupdate: improved help text for Lua support

It now explains limitations of building against Lua < 5.2 interpreters
and how to link to LuaJIT library.

Signed-off-by: Jordan Yelloz <jordan@yelloz.me>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/swupdate/Config.in

@@ -19,7 +19,11 @@ config BR2_PACKAGE_SWUPDATE
 	  use your own modified configuration, you have to select the
 	  necessary packages manually:
 
-	  * Select BR2_PACKAGE_LUA if you want to have Lua support.
+	  * Select BR2_PACKAGE_LUA or BR2_PACKAGE_LUAJIT if you want
+	    to have Lua support.
+	    CONFIG_HANDLER_IN_LUA is not supported in LuaJIT or Lua 5.1.
+	    Note that for LuaJIT support, you need to set
+	    CONFIG_LUAVERSION="jit-5.1".
 	  * Select BR2_LIBCURL if you want to use the download feature.
 	  * Select BR2_PACKAGE_OPENSSL is you want to add encryption support.
 	  * Select BR2_PACKAGE_MTD if you want to use swupdate with UBI