docs(tutorial/tutorial): instructions to install npm on debian

Additional package required for a Debian install

Closes angular#9749

Author: alindberg

docs/content/tutorial/index.ngdoc

@@ -110,8 +110,9 @@ suggested solution is to also install the `nodejs-legacy` apt package, which ren
 `nodejs`.
 
 ```
-apt-get install nodejs-legacy
+apt-get install nodejs-legacy npm
 nodejs --version
+npm --version
 ```