Update ADOPTERS.md
adding mattepaint.com to ADOPTERS.md
- [Kairos](https://kairos.com)
- [Kurio](https://kurio.id)
- [LeadIQ](https://leadiq.com)
+- [MattePaint](https://www.mattepaint.com/)
- [Mulligan Funding](https://www.mulliganfunding.com/)
- [National Information Solutions Cooperative (NISC)](https://nisc.coop/)
- [Nordstrom](https://nordstrom.com/)
