Update implicit-global warning message

Author: Sainan

docs/New Features/Compiler Warnings.md

@@ -188,7 +188,7 @@ a = 1
 ```
 file.pluto:3: warning: implicit global creation [implicit-global]
     3 | a = 1
-      | ^^^^^ here: prefix this with 'global' if creating a global was intended
+      | ^^^^^ here: prefix this with 'global' to be explicit
 ```
 
 ### discarded-return

docs/New Features/Explicit Globals.md

@@ -31,5 +31,5 @@ a = 1
 ```
 file.pluto:3: warning: implicit global creation [implicit-global]
     3 | a = 1
-      | ^^^^^ here: prefix this with 'global' if creating a global was intended
+      | ^^^^^ here: prefix this with 'global' to be explicit
 ```