add: Follower fetching image

[harshini-rangaswamy]

Describe your changes

Added an image to the "How it works" section of the Follower fetching concept topic.

Checklist

• The first paragraph of the page is on one line.
• The other lines have a line break at 90 characters.
• I checked the output.
• I applied the style guide.
• My links start with /docs/.

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[wojcik-dorota]

LGTM! If you'd like to have the images larger on the doc page, you might consider splitting them into separate tabs so that each of them can stretch to the page width.

[harshini-rangaswamy]

LGTM! If you'd like to have the images larger on the doc page, you might consider splitting them into separate tabs so that each of them can stretch to the page width.

Thanks! It is actually one image showing the difference between standard Kafka consumers vs. Follower fetching Kafka consumers.