Fix CLI dependency installation instructions (#1439)

vkentta · web-flow · commit c35cb7184490 · 2021-12-17T16:39:58.000+03:00
Without `postcss` fails with error:
`Error [ERR_MODULE_NOT_FOUND]: Cannot find package 'postcss' `
diff --git a/README.md b/README.md
@@ -355,7 +355,7 @@ module.exports = {
 You can use the [postcss-cli] to run Autoprefixer from CLI:
 
 ```sh
-npm install postcss-cli autoprefixer
+npm install postcss postcss-cli autoprefixer
 npx postcss *.css --use autoprefixer -d build/
 ```
 
