Disable lockbot comments and add notes in the contribution docs (#4508)

.github/lock.yml

@@ -18,15 +18,7 @@ exemptLabels: []
 lockLabel: outdated
 
 # Comment to post before locking. Set to `false` to disable
-lockComment: |
-  This thread has been automatically locked since there has not been
-  any recent activity after it was closed. Please open a [new issue] for
-  related bugs.
-
-  If you feel like there's important points made in this discussion,
-  please include those exceprts into that [new issue].
-
-  [new issue]: https://github.com/aio-libs/aiohttp/issues/new
+lockComment: false
 
 # Assign `resolved` as the reason for locking. Set to `false` to disable
 setLockReason: true

CHANGES/4504.doc

@@ -0,0 +1 @@
+Updated the contribution guide to reflect the automatic thread locking policy.

docs/contributing.rst

@@ -37,6 +37,16 @@ Workflow is pretty straightforward:
    needed. The Pull Request is automatically squashed into the single commit
    once the PR is accepted.
 
+.. note::
+
+   GitHub issue and pull request threads are automatically locked when there has
+   not been any recent activity for one year.  Please open a `new issue
+   <https://github.com/aio-libs/aiohttp/issues/new>`_ for related bugs.
+
+   If you feel like there are important points in the locked discussions,
+   please include those exceprts into that new issue.
+
+
 Preconditions for running aiohttp test suite
 --------------------------------------------