Switched references of App veyor to azure pipelines in the contributi…

…ng CI section (pandas-dev#23311)

doc/source/contributing.rst

@@ -657,12 +657,12 @@ Testing With Continuous Integration
 -----------------------------------
 
 The *pandas* test suite will run automatically on `Travis-CI <https://travis-ci.org/>`__,
-`Appveyor <https://www.appveyor.com/>`__, and `Circle CI <https://circleci.com/>`__ continuous integration
-services, once your pull request is submitted.
+`Azure Pipelines <https://azure.microsoft.com/en-us/services/devops/pipelines/>`__,
+and `Circle CI <https://circleci.com/>`__ continuous integration services, once your pull request is submitted.
 However, if you wish to run the test suite on a branch prior to submitting the pull request,
 then the continuous integration services need to be hooked to your GitHub repository. Instructions are here
 for `Travis-CI <http://about.travis-ci.org/docs/user/getting-started/>`__,
-`Appveyor <https://www.appveyor.com/docs/>`__ , and `CircleCI <https://circleci.com/>`__.
+`Azure Pipelines <https://docs.microsoft.com/en-us/azure/devops/pipelines/>`__, and `CircleCI <https://circleci.com/>`__.
 
 A pull-request will be considered for merging when you have an all 'green' build. If any tests are failing,
 then you will get a red 'X', where you can click through to see the individual failed tests.
@@ -672,8 +672,8 @@ This is an example of a green build.
 
 .. note::
 
-   Each time you push to *your* fork, a *new* run of the tests will be triggered on the CI. Appveyor will auto-cancel
-   any non-currently-running tests for that same pull-request. You can enable the auto-cancel feature for
+   Each time you push to *your* fork, a *new* run of the tests will be triggered on the CI.
+   You can enable the auto-cancel feature, which removes any non-currently-running tests for that same pull-request, for
    `Travis-CI here <https://docs.travis-ci.com/user/customizing-the-build/#Building-only-the-latest-commit>`__ and
    for `CircleCI here <https://circleci.com/changelog-legacy/#option-to-auto-cancel-redundant-builds>`__.