Update link to notes about usage as context manager (#313)

Fix #312

Author: nicoddemus

src/pytest_mock/plugin.py

@@ -213,7 +213,7 @@ def _start_patch(
                         "Mocks returned by pytest-mock do not need to be used as context managers. "
                         "The mocker fixture automatically undoes mocking at the end of a test. "
                         "This warning can be ignored if it was triggered by mocking a context manager. "
-                        "https://github.com/pytest-dev/pytest-mock#note-about-usage-as-context-manager",
+                        "https://pytest-mock.readthedocs.io/en/latest/remarks.html#usage-as-context-manager",
                         PytestMockWarning,
                         stacklevel=depth,
                     )

tests/test_pytest_mock.py

@@ -884,7 +884,7 @@ def doIt(self):
         "Mocks returned by pytest-mock do not need to be used as context managers. "
         "The mocker fixture automatically undoes mocking at the end of a test. "
         "This warning can be ignored if it was triggered by mocking a context manager. "
-        "https://github.com/pytest-dev/pytest-mock#note-about-usage-as-context-manager"
+        "https://pytest-mock.readthedocs.io/en/latest/remarks.html#usage-as-context-manager"
     )
 
     with pytest.warns(
@@ -901,7 +901,7 @@ def test_warn_patch_context_manager(mocker: MockerFixture) -> None:
         "Mocks returned by pytest-mock do not need to be used as context managers. "
         "The mocker fixture automatically undoes mocking at the end of a test. "
         "This warning can be ignored if it was triggered by mocking a context manager. "
-        "https://github.com/pytest-dev/pytest-mock#note-about-usage-as-context-manager"
+        "https://pytest-mock.readthedocs.io/en/latest/remarks.html#usage-as-context-manager"
     )
 
     with pytest.warns(