Config.in.legacy: update description for users

This patch clarifies the message shown to users in the legacy menu.
It explicitly mentions the need to save the configuration before disabling the
legacy options.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
diff --git a/Config.in.legacy b/Config.in.legacy
index 18224a0..237b8d0 100644
--- a/Config.in.legacy
+++ b/Config.in.legacy
@@ -69,11 +69,27 @@
 
 if BR2_LEGACY
 comment "Your old configuration uses legacy options that no  "
-comment "longer exist in buildroot.                          "
-comment "Please look at the options which have been selected "
-comment "and read their help text.                           "
-comment "As long as these options stay selected, the build   "
+comment "longer exist in buildroot, as indicated in the menu "
+comment "below. As long as these options stay selected, or in"
+comment "case of string options are non-empty, the build     "
 comment "will fail.                                          "
+comment "*                                                   "
+comment "Where possible, an automatic conversion from old to "
+comment "new symbols has been performed. Before making any   "
+comment "change in this legacy menu, make sure to exit the   "
+comment "configuration editor a first time and save the      "
+comment "configuration. Otherwise, the automatic conversion  "
+comment "of symbols will be lost.                            "
+comment "*                                                   "
+comment "After this initial save, reopen the configuration   "
+comment "editor, inspect the options selected below, read    "
+comment "their help texts, and verify/update the new         "
+comment "configuration in the corresponding configuration    "
+comment "menus. When everything is ok, you can disable the   "
+comment "legacy options in the menu below. Once you have     "
+comment "disabled all legacy options, this text will         "
+comment "disappear and you will be able to start the build.  "
+comment "*                                                   "
 comment "Note: at some point in the future, the oldest legacy"
 comment "options will be removed, and configuration files    "
 comment "that still have those options set, will fail to     "