docs(participant): add k6

[devtayls]

• [ x ] I have read and understand the Contributing.md requirements
• [ x ] I do not intend to make low-value changes, just for swag. I am aware that my PR could otherwise be flagged as spam or invalid and may lead to permanent exclusion from the Hacktoberfest event.

Adding a new Hacktoberfest participant

• [ x ] I did not edit the README.md file by hand
• [ x ] I have checked to ensure the new participant is not a duplicate and has not already been added
• [ x ] I am not adding a company from the blocklist
• [ x ] I have added the participant according to the Contributing.md requirements

Updating an existing Hacktoberfest participant

• I did not edit the README.md file by hand
• I have updated the existing participant.yml file according to the Contributing.md requirements

Updating the README.md

• I have discussed and received approval from a maintainer (@benbarth, @SoftCreatR, or @crweiner)

[devtayls]

@SoftCreatR The blog post has an embedded link to the repos participating:

https://github.com/grafana?q=k6+hacktoberfest&type=public&language=&sort=

Is there a way to embed the link? Or should I update the text to specify the repos? Or is it good as-is?

[SoftCreatR]

That's fine, i guess.