add draft to guidelines from slack discussion

sites/docs/src/content/docs/tutorials/contributing_to_nf-core/contributing_to_pipelines.md

@@ -19,8 +19,9 @@ The main steps involved in adding a new nf-core pipeline covered below are:
 2. [Contribution overview](#contribution-overview)
 3. [Testing](#testing)
 4. [Patching bugs](#patching-bugs)
-5. [Getting help](#getting-help)
-6. [Pipeline contribution conventions](#pipeline-contribution-conventions)
+5. [PR review guidelines](#pr-review-guidelines)
+6. [Getting help](#getting-help)
+7. [Pipeline contribution conventions](#pipeline-contribution-conventions)
 
 ## Join the community
 
@@ -42,7 +43,7 @@ If you'd like to write some code for an nf-core pipeline, the standard workflow
 2. [Fork](https://help.github.com/en/github/getting-started-with-github/fork-a-repo) the pipeline repository to your GitHub account
 3. Make the necessary changes / additions on `dev` branch by using [git checkout](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/committing-changes-to-a-pull-request-branch-created-from-a-fork) within your forked repository following [pipeline conventions](#pipeline-contribution-conventions)
 4. Use `nf-core pipelines schema build` and add any new parameters to the pipeline JSON schema (requires [nf-core tools](https://github.com/nf-core/tools) >= 1.10).
-5. Submit a Pull Request against the `dev` branch and wait for the code to be reviewed and merged
+5. Submit a Pull Request against the `dev` branch and wait for the code to be reviewed and merged. See below guidelines for this.
 
 If you're new to working with git, you can view the [GitHub pull requests documentation](https://help.github.com/en/github/collaborating-with-issues-and-pull-requests) or other [excellent `git` resources](https://try.github.io/) to get started.
 
@@ -80,6 +81,22 @@ Only in the unlikely and regretful event of a release happening with a bug.
 - Fix the bug, and bump version (X.Y.Z+1).
 - A PR should be made on `master` from patch to directly resolve this particular bug.
 
+## PR review guidelines
+
+- Authors/Reviewers can request help for review at nf-core Slack `#request-review` channel.
+- We encourage collaboration in PR, other contributors are welcome to fix linting errors (you can mention relevant bot commands) or make improvements to the code if necessary.
+- Authors/Reviewers should merge after one positive review and with no obvious open questions.
+  - Exception: merges to master for releases requires **two** reviews.
+  - Exception: pseudo PR reviews for a first release needs **review from core or maintainer team**.
+  - If it's there is a major change in any type of PR (from modules to pipelines) then it's ok to request a second review - either the author or reviewer can do this.
+  - PRs that have approving reviews but remaining open questions can be merged by the author after addressing the questions to a common-sense level of satisfaction.
+  - If the reviewer feels uneasy about this then they shouldn't leave an approval, but rather a request-changes.
+  - **request changes** reviews can be [dismissed](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/dismissing-a-pull-request-review) by the PR author if considered out of date and resolved.
+- We prefer to use merge commits to merge. This is to avoid merge conflicts when multiple people are pulling with overlapping feature branches.
+  - We prefer verbose commit histories but easy merges.
+  - Feature branches should be immediately deleted after merge. Ideally by selecting the new feature on GitHub repo settings
+  - Note: squashing commits in a PR and merging after is fine, that is up to the individuals.
+
 ## Getting help
 
 For further information/help, please consult the usage documentation for the particular pipeline and don't hesitate to get in touch on the nf-core Slack `#<pipeline-name>` channel. If you are not already a member you can ([join our Slack here](https://nf-co.re/join/slack)).