patch: update SRE ressources

remove reference to heroku as we're not longer use it

docs/sre-resources.md

@@ -24,9 +24,7 @@ While our overall [product surface](https://docs.google.com/drawings/d/1SBDms6dA
 
 * ARM architecture builders hosted on [Equinix](https://www.equinix.com/)
 * Kubernetes (k8s) cluster(s)
-* [CloudFlare](https://dash.cloudflare.com/) 
-* [Hubot](https://github.com/balena-io/hubot-as-mainbot) hosted at [Heroku](https://www.heroku.com/)
-* balena.io blog and website in [Netlify](https://netlify.com/)
+* [CloudFlare](https://dash.cloudflare.com/)
 
 
 #### CI/CD
@@ -44,12 +42,12 @@ While our overall [product surface](https://docs.google.com/drawings/d/1SBDms6dA
 * [Sentry](https://sentry.io/organizations/balena/issues/) front-end logging
 * [Logentries](https://logentries.com/app/5915e005) back-end logging
 * [statuspage.io](https://manage.statuspage.io/pages/5b4dcn321xtp) customer facing status page
-* [Nodeping](https://nodeping.com/) TBC/legacy?
-* [healthchecks.io](https://healthchecks.io/accounts/login/) TBC/legacy?
+* [Nodeping](https://nodeping.com/)
+* [healthchecks.io](https://healthchecks.io/accounts/login/) (probably optional)?
 
 
 #### balena|product
 * JellyFish
 * personal account (e.g. GitHub linked) [balenaCloud](https://dashboard.balena-cloud.com/apps) team member group membership
 * company account (e.g. G Suite linked) [balenaCloud](https://dashboard.balena-cloud.com/apps) support agent permission
-* [balenaStaging](https://dashboard.balena-staging.com/apps) and [admin](https://admin.balena-staging.com/) support agent permission
+* [balenaStaging](https://dashboard.balena-staging.com/apps) and [admin](https://admin.balena-staging.com/) support agent permission