Explain how to install the schematics package in Readme (#2018)

`ng add ng2-charts` does not seem to do it, so installing/adding it may be useful, is not it? Also maybe add it to the website?

Note it should work, however, see #2017

Co-authored-by: Alexey Umanskiy <sharkakatsukie@gmail.com>

Author: rklec

README.md

@@ -21,6 +21,11 @@ ng add ng2-charts
 The required packages will be automatically installed, and your `app.config.ts` will be updated with the required
 changes to start using the library right away.
 
+If you want to install [schematics](https://www.npmjs.com/package/ng2-charts-schematics) for easier code generation too:
+```bash
+npm install --save-dev ng2-charts-schematics
+```
+
 #### Manual install through package managers
 
 1. You can install **_ng2-charts_** using npm: