Add DigitalOcean to the adopters list. (#1765)

Have a signoff from @thorfour

Signed-off-by: Goutham Veeramachaneni <[email protected]>

Author: gouthamve

ADOPTERS.md

@@ -3,6 +3,7 @@
 This is the list of organisations that are using Cortex in **production environments** to power their metrics and monitoring systems. Please send PRs to add or remove organisations.
 
 * [Aspen Mesh](https://aspenmesh.io/)
+* [DigitalOcean](https://www.digitalocean.com/)
 * [Electronic Arts](https://www.ea.com/)
 * [GoJek](https://www.gojek.io/)
 * [GrafanaLabs](https://grafana.com/)