diff --git a/README.md b/README.md
index 7a8b1ec..8c0c5c4 100644
--- a/README.md
+++ b/README.md
@@ -13,7 +13,8 @@ I dunno, cause I wanted to play with these sensors and keep track of the air qua
 ### Prep
 
 You need to have the pico-sdk installed. I have it installed in ~/workspace/rp2040/pico-sdk and this is currently hard-coded into CMakeFiles.txt. I'm not sure if exporting an environment variable overrides this by default, but you can always just edit it to point to wherever you have it installed.
-You also need to create a file in include/ called credentials.h in the following format:
+
+You also **must** create a file in include/ called credentials.h in the following format:
 
 ```c
 #ifndef CREDENTIALS_H
@@ -30,6 +31,8 @@ You also need to create a file in include/ called credentials.h in the following
 
 This keeps your credentials separate from the git history in case you want to make/submit changes. The build will fail if you don't create this file and define those four things.
 
+You'll also need to edit src/main.c and change the MQTT topic names to whatever you are using.
+
 ### Build
 
 Create a new directory in the project called build. Move into that directory and run: