Add generateTip function

[heatem]

In the generateTip function in the app.js file:

• Add a constant named randomTip that is a random integer between 0 and
• the length of the tips array
• Using randomTip, show the tipText in the paragraph with the tip ID
• Using randomTip, if there is a link url, add it to the paragraph with the link ID. The href should be set to the url. Show the link description if it exists, otherwise show the url. Clear the link paragraph if the tip doesn't include link data.
• Using randomTip, show the contributor in the paragraph with the contributor ID
• Delete the related TODOs