Update HELLO.md

[angelikatyborska]

• Fixes outdated links
• Stops talking about v3 and using the future tense, the future is now!
• Removes the task to port an exercise from problem specifications because those have been depleted 😬

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[jiegillet]

Removes the task to port an exercise from problem specifications because those have been depleted 😬

Sorry, not sorry ;)