docs: update contributing and membership links (#1702)

Author: rogercoll

CONTRIBUTING.md

@@ -2,9 +2,9 @@
 
 Welcome to OpenTelemetry Demo Webstore repository!
 
-Before you start - see OpenTelemetry general
-[contributing](https://github.com/open-telemetry/community/blob/main/CONTRIBUTING.md)
-requirements and recommendations.
+Before you start - see OpenTelemetry
+ [Contributor Guide](https://github.com/open-telemetry/community/blob/main/guides/contributor/README.md)
+ for details on code attribution.
 
 ## Join a SIG Call
 
@@ -167,9 +167,9 @@ Open a pull request against the main `opentelemetry-demo` repo.
 A PR is considered to be **ready to merge** when:
 
 - It has received approval from
-  [Approvers](https://github.com/open-telemetry/community/blob/main/community-membership.md#approver)
+  [Approvers](https://github.com/open-telemetry/community/blob/main/guides/contributor/membership.md#approver)
   /
-  [Maintainers](https://github.com/open-telemetry/community/blob/main/community-membership.md#maintainer).
+  [Maintainers](https://github.com/open-telemetry/community/blob/main/guides/contributor/membership.md#maintainer).
 - Major feedbacks are resolved.
 - It has been open for review for at least one working day. This gives people
   reasonable time to review.

README.md

@@ -77,14 +77,14 @@ Monday at 8:30 AM PST and anyone is welcome.
 
 ## Project leadership
 
-[Maintainers](https://github.com/open-telemetry/community/blob/main/community-membership.md#maintainer)
+[Maintainers](https://github.com/open-telemetry/community/blob/main/guides/contributor/membership.md#maintainer)
 ([@open-telemetry/demo-maintainers](https://github.com/orgs/open-telemetry/teams/demo-maintainers)):
 
 - [Juliano Costa](https://github.com/julianocosta89), Datadog
 - [Mikko Viitanen](https://github.com/mviitane), Dynatrace
 - [Pierre Tessier](https://github.com/puckpuck), Honeycomb
 
-[Approvers](https://github.com/open-telemetry/community/blob/main/community-membership.md#approver)
+[Approvers](https://github.com/open-telemetry/community/blob/main/guides/contributor/membership.md#approver)
 ([@open-telemetry/demo-approvers](https://github.com/orgs/open-telemetry/teams/demo-approvers)):
 
 - [Cedric Ziel](https://github.com/cedricziel) Grafana Labs