Document merge barriers (#707)

* Document merge barriers

* Document remedy

* s/PR/pull request/g

* Document merge barriers on their own page

* Fix links

* Try .md suffix

Author: KyleFromNVIDIA

resources/merge-barriers.md

@@ -0,0 +1,48 @@
+---
+layout: default
+nav_order: 6
+parent: Resources
+grand_parent: Maintainer Docs
+title: Merge Barriers
+---
+
+# _Merge Barriers_ Check
+
+## Overview
+
+A GitHub action that checks whether a pull-request is up-to-date with the any merge barrier commits from the source repository.
+
+### Intended audience
+
+Community
+{: .label .label-yellow}
+
+Developers
+{: .label .label-green}
+
+Project Leads
+{: .label .label-blue}
+
+Operations
+{: .label .label-purple}
+
+## Summary
+
+Pull requests can be explicitly marked as "merge barriers" to be required to be merged into a pull request before it can be merged. This is used for pull requests that have wide-reaching implications, such as broad reformatting or linting, which are highly likely to cause logical merge conflicts with many other pull requests.
+
+The _Merge Barriers_ check is configurable by editing the following value in the `.github/ops-bot.yaml` file:
+
+```yaml
+# enables/disables the Merge Barriers Check
+merge_barriers: true
+```
+
+A pull request can be marked as a merge barrier by adding the following line to the description:
+
+```
+Ops-Bot-Merge-Barrier: true
+```
+
+If a pull request with this line is merged, no pull requests can be merged after it unless they merge in the merge barrier commit. If a pull request cannot be merged due to missing a merge barrier, the easiest fix is to simply merge in the latest commit from the target branch.
+
+For more generic requirements to keep a pull request reasonably up-to-date with the origin, see the [recently updated check](./recently-updated.md).

resources/recently-updated.md

@@ -52,3 +52,5 @@ recently_updated_threshold: 5
 ```
 
 Note that since RAPIDS uses squash commits for pull requests, the `recently_updated_threshold` value effectively means "how many pull requests have been merge into the source repository since the current pull request has last been updated".
+
+For more specific control over which commits need to be merged into pull requests, see [merge barriers](./merge-barriers.md).

resources/reproducing-ci.md

@@ -141,7 +141,7 @@ gh auth login
 NOTE: On shared machines, this method might expose your GitHub token in the output of `ps`. In those settings,
 consider just relying on the interactive prompts inside the container or using the `--env-file` approach.
 
-For more details, see "GitHub Actions" ([link](./github-actions)).
+For more details, see "GitHub Actions" ([link](./github-actions.md)).
 
 ### Downloading Build Artifacts for Tests