[cqfn#201] update readme

README.md

@@ -68,10 +68,16 @@ pdd --include=src/**/* # include all files in src/
 
 `` --model ``
 
-Opt-in to use inbuilt ML model to prioritize puzzles found in code. 
+The `--model` flag used by [0pdd](https://github.com/yegor256/0pdd#readme) to opt-in to use ML model which prioritizes puzzles generated by `pdd`. Therefore, this flag is only a marker for the [0pdd](https://github.com/yegor256/0pdd#readme) service. If you use 0pdd and you want to opt-in to puzzle prioritization, then add this flag to your `.pdd` config file in your project.
+```bash
+# ~/.pdd config file
+--model
+```
+
+You can also use the [pdd gem](https://rubygems.org/gems/pdd) directly;
 ```bash
 pdd --model
-pdd -m
+pdd -m 
 ```
 
 ## How to Format?