docs: add section on ci tags available in pmaports

Fixes https://gitlab.postmarketos.org/postmarketOS/docs.postmarketos.org/-/issues/13

Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/7336>

docs/ci-tags.md

@@ -0,0 +1,25 @@
+# CI tags
+
+You can add various tags in the commit message of your last commit  to modify
+the continuous integration behaviour for your merge requests:
+
+* `[ci:skip-build]`: Do not build modified packages, only verify their
+  checksums. Use this when pushing changes to an MR that should not trigger a
+  complete build.
+* `[ci:ignore-count]`: Allow skipping the "too many packages changed" check.
+  Use this when automatically modifying many device packages.
+* `[ci:skip-vercheck]`: Do not verify if the version of a changed package has
+  been increased. Use this, when making a cosmetic change in an APKBUILD that
+  should not cause the package to get rebuilt, or when changing the enabled
+  architectures.
+* `[ci:skip-kconfigcheck]`: Do not check the kernel config for packages
+  changed in the commit. Use this when moving kernel packages between
+  categories or performing bulk changes across a lot of kernel packages, but
+  never when upgrading the kernel.
+* `[ci:skip-dint]`: Do not run the device-linter check. Use this when moving
+  or modifying many devices not maintained by you that due to historical reasons
+  might not pass the check.
+* `[skip ci]`: Completely skip the pipeline for the merge request. This is a
+  GitLab [feature](https://docs.gitlab.com/ci/pipelines/#skip-a-pipeline). Use
+  this only in very extreme situations where CI might be broken, but a change is
+  needed to fix critical bugs. Whenever possible, try to use the other tags.

docs/index.md

@@ -15,6 +15,6 @@ in pmaports and the processes around device categorization.
 
    approval-rules
    device-categorization
+   ci-tags
    kernel-versions
 ```
-