Give more helpful warning about setting HOME

* src/w32.c (init_environment): Improve warning message that pops when
Emacs sets HOME according to existence of C:\.emacs (Bug #11612).

Co-authored-by: Eli Zaretskii <eliz@gnu.org>

src/w32.c

@@ -2773,10 +2773,13 @@ init_environment (char ** argv)
 		  }
 		if (strcmp (env_vars[i].name, "HOME") == 0 && !appdata)
 		  Vdelayed_warnings_list
-		    = Fcons (listn (CONSTYPE_HEAP, 2,
-				    intern ("initialization"),
-				    build_string ("Setting HOME to C:\\ by default is deprecated")),
-			     Vdelayed_warnings_list);
+                    = Fcons
+                    (listn (CONSTYPE_HEAP, 2,
+                            intern ("initialization"), build_string
+                            ("Use of `C:\\.emacs' without defining `HOME' "
+                             "in the environment is deprecated,\n"
+                             "see `Windows Home' in the Emacs manual."))),
+                    Vdelayed_warnings_list);
 	      }
 
 	    if (lpval)