Update community-slack.md

[Anurag0git]

List the key channels on the Slack channels page issue #96 resolved

[oleg-nenashev]

Thank you for the list, I will take it from there! I do not think all channels should be here on the list, and ordering needs an update. I will think about it and update it accordingly

[Anurag0git]

Thank you for the list, I will take it from there! I do not think all channels should be here on the list, and ordering needs an update. I will think about it and update it accordingly

i would be grateful if you would add hactoberfest label and merge it

[oleg-nenashev]

Thanks for the patch @Anurag0git !