diff --git a/README.md b/README.md
index a8c64ed..7a8b1ec 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,23 @@ 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:
+
+```c
+#ifndef CREDENTIALS_H
+#define CREDENTIALS_H
+
+// Replace these placeholders with your actual credentials
+#define ADAFRUIT_IO_USERNAME "your-username"
+#define ADAFRUIT_IO_KEY      "your-adafruit-io-key"
+#define WIFI_SSID            "wifi-ssid"
+#define WIFI_PASSWORD        "wifi-password"
+
+#endif // CREDENTIALS_H
+```
+
+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.
+
 ### Build
 
 Create a new directory in the project called build. Move into that directory and run: