Add contribution merging consideration (privacy-scaling-explorations#480

)

CONTRIBUTING.md

@@ -15,6 +15,7 @@ Before starting, we encourage you to take a look to the following documentation
 It's up to the mantainers to decide whether more than one review is required.
 - Avoid requesting reviews of a PR in `zkevm-circuits` when the implementation follows a spec that is not yet in `master` at `zkevm-specs`.  In such case, set the `zkevm-circuits` PR as draft to signal you're working on it but it's not yet ready for review.
 - Provide clear title and description of any PR and/or Issue you raise. That helps a lot to the reviewers/mantainers and other contributors to understand it's scope and purpose.
+- The author of the PR should be the one to merge their own PR after the required approvals.  Only when the author has no merge permission will a reviewer perform the merge.
 
 ## Opcodes
 
@@ -23,4 +24,4 @@ It's up to the mantainers to decide whether more than one review is required.
     2. After the spec is merged, implement the opcode and submit a PR in `zkevm-circuits`
         - It's OK to work on the circuit and spec at the same time and have the implementation PR submitted before the spec is merged, but in such case, please set the implementation PR as draft until the spec is merged.
 
-- Try to include `bus-mapping` + `zkevm-circuits` opcode implementations in the same PR, but never mixing more than one Opcode at a time.
+- Try to include `bus-mapping` + `zkevm-circuits` opcode implementations in the same PR, but never mixing more than one Opcode at a time.