feat: add Samples section to CONTRIBUTING.rst (#229)

Source-Link: https://github.com/googleapis/synthtool/commit/52e4e46eff2a0b70e3ff5506a02929d089d077d4
Post-Processor: gcr.io/repo-automation-bots/owlbot-python:latest@sha256:6186535cbdbf6b9fe61f00294929221d060634dae4a0795c1cefdbc995b2d605
diff --git a/.github/.OwlBot.lock.yaml b/.github/.OwlBot.lock.yaml
index cb06536..d57f742 100644
--- a/.github/.OwlBot.lock.yaml
+++ b/.github/.OwlBot.lock.yaml
@@ -1,3 +1,3 @@
 docker:
   image: gcr.io/repo-automation-bots/owlbot-python:latest
-  digest: sha256:5ff7446edeaede81c3ed58b23a4e76a5403fba1350ce28478045657303b6479d
+  digest: sha256:6186535cbdbf6b9fe61f00294929221d060634dae4a0795c1cefdbc995b2d605
diff --git a/CONTRIBUTING.rst b/CONTRIBUTING.rst
index 07c9a61..c7860ad 100644
--- a/CONTRIBUTING.rst
+++ b/CONTRIBUTING.rst
@@ -177,6 +177,30 @@
 
    $ nox -s docs
 
+*************************
+Samples and code snippets
+*************************
+
+Code samples and snippets live in the `samples/` catalogue. Feel free to
+provide more examples, but make sure to write tests for those examples.
+Each folder containing example code requires its own `noxfile.py` script
+which automates testing. If you decide to create a new folder, you can
+base it on the `samples/snippets` folder (providing `noxfile.py` and
+the requirements files).
+
+The tests will run against a real Google Cloud Project, so you should
+configure them just like the System Tests.
+
+- To run sample tests, you can execute::
+
+   # Run all tests in a folder
+   $ cd samples/snippets
+   $ nox -s py-3.8
+
+   # Run a single sample test
+   $ cd samples/snippets
+   $ nox -s py-3.8 -- -k <name of test>
+
 ********************************************
 Note About ``README`` as it pertains to PyPI
 ********************************************