fix Issue 23694 and Issue 23700 Document ImportC CTFE

Author: WalterBright

spec/importc.dd

@@ -424,8 +424,20 @@ int myprintf(char *, ...) asm("printf");
     $(H3 $(LNAME2 ctfe, Compile Time Function Execution))
 
     $(P Evaluating constant expressions includes executing functions in the
-    same manner as D's CTFE can.)
+    same manner as D's CTFE can.
+    A $(I constant-expression) invokes CTFE.)
 
+    $(P Examples:)
+
+$(CCODE
+_Static_assert("\x1"[0] == 1, "failed");
+
+int mint1() { return -1; }
+_Static_assert(mint1() == -1, "failed");
+
+const int a = 7;
+int b = a; // sets b to 7
+)
 
     $(H3 $(LNAME2 inlining, Function Inlining))