Update community guidelines to prohibit DM solicitation

[Copilot]

Community members are receiving unwanted DMs asking for personal/professional info, profile links, and unsolicited collaboration requests.

Changes to slack/guidelines.md

Code of Conduct - Inappropriate behaviour:

• Asking for personal or professional details in DM (location, current job, skills)
• Asking people to share their profiles (LinkedIn, Upwork)
• Offering collaboration in DM without prior public communication

Unsolicited promotions section:

• Added explicit rule requiring public channel engagement before DM collaboration requests

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update community guidelines</issue_title>
<issue_description>We don't want people writing in DM asking location, current job or skills. We don't want people asking to reveal their profiles like LinkedIn or upwork. We don't want people offering collaboration in DM without prior communication outside of DM.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Update community guidelines #99

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