Add example plugin from certbot source, and notes for running with certbot docker container

.gitignore

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+*.pyc
+*.pyo
+*.swp
+*.swo
+*.egg-info
+

certbot-example-plugins/certbot_example_plugins.py

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+"""Example Certbot plugins.
+
+For full examples, see `certbot.plugins`.
+
+"""
+import zope.interface
+
+from certbot import interfaces
+from certbot.plugins import common
+
+
+@zope.interface.implementer(interfaces.IAuthenticator)
+@zope.interface.provider(interfaces.IPluginFactory)
+class Authenticator(common.Plugin):
+    """Example Authenticator."""
+
+    description = "Example Authenticator plugin"
+
+    # Implement all methods from IAuthenticator, remembering to add
+    # "self" as first argument, e.g. def prepare(self)...
+
+
+@zope.interface.implementer(interfaces.IInstaller)
+@zope.interface.provider(interfaces.IPluginFactory)
+class Installer(common.Plugin):
+    """Example Installer."""
+
+    description = "Example Installer plugin"
+
+    # Implement all methods from IInstaller, remembering to add
+    # "self" as first argument, e.g. def get_all_names(self)...

certbot-example-plugins/setup.py

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+from setuptools import setup
+
+
+setup(
+    name='certbot-example-plugins',
+    package='certbot_example_plugins.py',
+    install_requires=[
+        'certbot',
+        'zope.interface',
+    ],
+    entry_points={
+        'certbot.plugins': [
+            'example_authenticator = certbot_example_plugins:Authenticator',
+            'example_installer = certbot_example_plugins:Installer',
+        ],
+    },
+)

notes.txt

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+docker run -it --rm --entrypoint /bin/sh -v "$(pwd)/certbot-example-plugins:/tmp/certbot-example-plugins"  certbot/certbot:v0.22.0
+certbot plugins
+pip install -e /tmp/certbot-example-plugins