Promote paper event submission

[annakrystalli]

• [x] RSE Sheffield Newsletter
• [x] RSE Sheffield Team
• [x] RSE Slack
• [x] ReproHack Slack
• [x] SSI Slack
• [x] Twitter
• [x] HCC Chairs
• [x] Archer User Mailing
• [x] N8 Newsletter
• [x] Linkedin