Introduce script for installing all dependencies

Co-authored-by: Mikko Aspiala <mikko.aspiala@gmail.com>

Signed-off-by: Janne Savolainen <janne.savolainen@live.fi>

package.json

@@ -7,6 +7,7 @@
   ],
 
   "scripts": {
+    "all:install": "npm install",
     "adr:create": "echo \"What is the title?\"; read title; adr new \"$title\"",
     "adr:change-status": "echo \"Decision number?:\"; read decision; adr status $decision",
     "adr:update-readme": "adr update",