Add a new meetup to community section

[ljuti]

Adds Helsinki, Finland to community meetups page.

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[harish-sethuraman]

Can you resolve the conflicts? :) We can add Helsinki to the list ;)

[rickhanlonii]

Sorry for missing this in 2018. Looks like this meetup hasn't been active since 2020, and we just added react-helsinki in #7474.