docs: add a link to the cncf calendar for the community meeting (#4431)

docs/contributing/calendar.md

@@ -0,0 +1,5 @@
+# Community meetings - CNCF calendar
+
+ESO community calls can be subscribed to from the CNCF Project Calendar page here [CNCF Calendar](https://www.cncf.io/calendar/).
+
+Look for the event called `External Secrets Bi-weekly community meeting`.

hack/api-docs/mkdocs.yml

@@ -155,6 +155,7 @@ nav:
           - Contributing Process: contributing/process.md
           - Release Process: contributing/release.md
           - Code of Conduct: contributing/coc.md
+          - Community meetings calendar: contributing/calendar.md
           - Roadmap: contributing/roadmap.md
       - External Resources:
           - Talks: eso-talks.md