Document some of the regular admin tasks (#133825)

This is not everything, but it's a start.

llvm/docs/AdminTasks.rst

@@ -0,0 +1,48 @@
+================
+LLVM Admin Tasks
+================
+
+Commit Access Review
+--------------------
+
+* Frequency: Monthly
+* Permissions: Triage
+* Description: The `Commit Access Review <https://github.com/llvm/llvm-project/actions/workflows/commit-access-review.yml>`_
+  github actions job runs once per month and generates an artifact called 'triagers' which is a list of GitHub users who
+  no longer qualify for commit access due to limited activity over the last 12 months.
+
+When the job completes, an admin should download the triagers artifact and create an issue asking everyone on
+the list if they still need commit access.  Here is an `example issue <https://github.com/llvm/llvm-project/issues/131262>`_.
+The issue should have the 'infra:commit-access' label and should use the same description as the example issue.
+
+Removing Users from LLVM Committers team
+----------------------------------------
+
+* Frequencey: Monthly
+* Permissions: Admin
+* Description: Each month an admin should review any open issues with the infra:commit-access label.
+  For any issue that has been open for more than 4 weeks, any user who has not responded on the ticket
+  should be moved from the LLVM Committers team to the LLVM Triagers team.
+
+Action Secret Rotation
+----------------------
+
+* Frequency: Monthly
+* Permissions: Admin
+* Description: Each month an admin should rotate the secrets that are used for GitHub Actions workflows
+  in the llvm-project repository.
+
+The secrets are personal access tokens that are associated with the llvmbot GitHub account.  An admin
+should log in to the llvmbot account, re-generate the personal access tokens and then copy the
+new values into the corresponding secret in the llvm-project repo's settings.
+
+Grant Commit Access
+--------------------
+
+* Frequency: Ongoing
+* Permissions: Admin
+* Description: An admin should periodically review the list of commit access requests.  This can be
+  done by searching for issues in the llvm-project repository which have the infra:commit-access-request
+  label.  Any user that meets the `commit access requirements <https://llvm.org/docs/DeveloperPolicy.html#obtaining-commit-access>`_
+  should be added to the 'LLVM Committers' team.  The admin should add a comment to the issue when
+  an invite to join the team has been sent and then close the issue when the invite has been accepted.

llvm/docs/UserGuides.rst

@@ -14,6 +14,7 @@ intermediate LLVM representation.
 
    AArch64SME
    AddingConstrainedIntrinsics
+   AdminTasks
    AdvancedBuilds
    AliasAnalysis
    AMDGPUUsage