SCons: Identify build clearly when using AES256 encryption key

It seems to be a common pitfall that users try to build custom templates with a key
but somehow it doesn't get picked up as they expect it to.

Author: akien-mga

core/SCsub

@@ -185,9 +185,15 @@ gen_hash = env.CommandNoCache(
 env.add_source_files(env.core_sources, gen_hash)
 
 # Generate AES256 script encryption key
+encryption_key = os.environ.get("SCRIPT_AES256_ENCRYPTION_KEY")
+if encryption_key:
+    print(
+        "\n*** IMPORTANT: Compiling Godot with custom `SCRIPT_AES256_ENCRYPTION_KEY` set as environment variable."
+        "\n*** Make sure to use templates compiled with this key when exporting a project with encryption.\n"
+    )
 gen_encrypt = env.CommandNoCache(
     "script_encryption_key.gen.cpp",
-    env.Value(os.environ.get("SCRIPT_AES256_ENCRYPTION_KEY")),
+    env.Value(encryption_key),
     env.Run(core_builders.encryption_key_builder),
 )
 env.add_source_files(env.core_sources, gen_encrypt)