Add link and image of NumPy comics to Contribute page

[MarsBarLee]

I've added a link and image to the 'How to Contribute to NumPy' comic in the Contribute page.

However, the image is showing up as broken like this:

@Mukulikaa Could you take a look at this?

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[MarsBarLee]

I can also resize the image so it's smaller. The image is 780kB, I can make it smaller. The other image in the images folder is 150kB, so I can make the resized image around the same size.

[InessaPawson]

@MarsBarLee To keep things organized, please move the image to the static/images/content_images/ folder.

[InessaPawson]

I can also resize the image so it's smaller. The image is 780kB, I can make it smaller. The other image in the images folder is 150kB, so I can make the resized image around the same size.

@MarsBarLee A lighter image would be better. We prefer to keep them light to reduce load times.

[MarsBarLee]

@InessaPawson Thank you for the suggestions! I worked with Mukulika and we fixed the image so it would display properly and at the right size. I wasn't able to get my local development server to show the image but it shows up on Netlify.

The image size right now is hard-coded with pixels- would it be worthwhile to submit a separate PR with shortcode and flexible image size? I see on the About Us page, the sponsor images uses shortcode with sponsor.html.

I tried this shortcode method on a separate branch on my fork here.