Clarify the prototyping expectation (#3574)

.github/PULL_REQUEST_TEMPLATE.md

@@ -4,8 +4,10 @@ Fixes #
 
 Please provide a brief description of the changes here.
 
-For non-trivial changes, follow the [change proposal process](https://github.com/open-telemetry/opentelemetry-specification/blob/main/CONTRIBUTING.md#proposing-a-change) and link to the related issue(s) and/or [OTEP(s)](https://github.com/open-telemetry/oteps), update the [`CHANGELOG.md`](https://github.com/open-telemetry/opentelemetry-specification/blob/main/CHANGELOG.md), and also be sure to update [`spec-compliance-matrix.md`](https://github.com/open-telemetry/opentelemetry-specification/blob/main/spec-compliance-matrix.md) if necessary.
+For non-trivial changes, follow the [change proposal process](https://github.com/open-telemetry/opentelemetry-specification/blob/main/CONTRIBUTING.md#proposing-a-change).
 
-Related issues #
-
-Related [OTEP(s)](https://github.com/open-telemetry/oteps) #
+* [ ] Related issues #
+* [ ] Related [OTEP(s)](https://github.com/open-telemetry/oteps) #
+* [ ] Links to the prototypes (when adding or changing features)
+* [ ] [`CHANGELOG.md`](https://github.com/open-telemetry/opentelemetry-specification/blob/main/CHANGELOG.md) file updated for non-trivial changes
+* [ ] [`spec-compliance-matrix.md`](https://github.com/open-telemetry/opentelemetry-specification/blob/main/spec-compliance-matrix.md) updated if necessary

CONTRIBUTING.md

@@ -28,6 +28,10 @@ Smaller changes can follow a shorter process:
   may be opened and linked to the issue even before the proposed idea is accepted there.
 - Once the issue is accepted the assignee can work on it and create a PR that implements
   the change described in the issue.
+- In the PR description, provide links to the prototypes. Depending on the scope
+  of the change, prototyping in multiple programming languages might be required
+  by the [specification
+  approvers](https://github.com/open-telemetry/community/blob/main/community-members.md#specifications-and-proto).
 
 Trivial changes, such as clarifications, wording changes, spelling/grammar
 corrections, etc. can be made directly via pull requests and do not require an associated