colrv1/README.md: recommend to regenerate configs as initial step before build

colrv1/README.md

@@ -5,6 +5,16 @@ contains emojicompat metadata.
 
 ## Build Steps
 
+1. Check the list of sources in the config files is in sync with the current sources
+
+   ```shell
+   # running from the noto-emoji repository root directory
+   python colrv1_generate_configs.py
+   git diff colrv1/*.toml
+   ```
+
+   If configs are in sync, the `colrv1/*.toml` files should contain no diffs.
+
 1. Compile the COLRv1 fonts
 
    ```shell
@@ -18,4 +28,4 @@ contains emojicompat metadata.
    # Assumed to be in a python3 environment with requirements.txt fulfilled
    python colrv1_postproc.py colrv1/build/NotoColorEmoji-noflags.ttf \
    	PATH_TO/NotoColorEmojiCompat.ttf
-   ```
+   ```