Change Glitch signup to signin URL

Author: bcopy

en/chromebook_setup/instructions.md

@@ -64,7 +64,7 @@ bigger.
 #### Glitch.com Cloud IDE
 
 1. Go to [Glitch.com](https://glitch.com/)
-2. Sign up for an account (https://glitch.com/signin) or use your GitHub account if you have one (see GitHub instructions below).
+2. Sign up for an account (https://glitch.com/signup) or use your GitHub account if you have one (see GitHub instructions below).
 3. Click _New Project_ and choose _hello-webpage_
 4. Click on the `Tools` dropdown list (at the bottom left side of the window), then on `Terminal` button to open terminal tab with a prompt like this: