Add instructions on how to merge a PR (#85280)

Adding basic instructions for now
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85280
Approved by: https://github.com/malfet, https://github.com/huydhn, https://github.com/janeyx99

CONTRIBUTING.md

@@ -16,6 +16,7 @@
     - [Running `mypy`](#running-mypy)
   - [C++ Unit Testing](#c-unit-testing)
   - [Run Specific CI Jobs](#run-specific-ci-jobs)
+- [Merging your Change](#merging-your-change)
 - [Writing documentation](#writing-documentation)
   - [Docstring type formatting](#docstring-type-formatting)
   - [Building documentation](#building-documentation)
@@ -435,6 +436,17 @@ ghstack submit
 [`ghstack`](https://github.com/ezyang/ghstack). It creates a large commit that is
 of very low signal to reviewers.
 
+## Merging your Change
+If you know the right people or team that should approve your PR (and you have the required permisssions to do so), add them to the Reviewers list.
+
+If not, leave the Reviewers section empty. Our triage squad will review your PR, add a module label, and assign it to the appropriate reviewer in a couple business days.  The reviewer will then look at your PR and respond.
+
+Occasionally, things might fall through the cracks (sorry!). In case your PR either doesn't get assigned to a reviewer or doesn't get any response from the reviewer for 4 business days, please leave comment on the PR (mentioning the reviewer if one has been assigned). That'll get it nudged back onto people's radar.
+
+If that still doesn't help, come see us during [our office hours](https://github.com/pytorch/pytorch/wiki/Contact-Pytorch-Dev-Infra-Office)
+
+Once your PR is approved, you can merge it in by entering a comment with the content `@pytorchmergebot merge` ([what's this bot?](https://github.com/pytorch/pytorch/wiki/Bot-commands))
+
 ## Writing documentation
 
 So you want to write some documentation and don't know where to start?