update custom credential plugin docs to point at an example project

docs/credentials/credential_plugins.md

@@ -49,79 +49,7 @@ registered using setuptools entrypoints
 Example plugins officially supported in AWX can be found in the source code at
 `awx.main.credential_plugins`.
 
-Credential plugins are any Python object which defines attribute lookups for `.name`, `.inputs`, and `.backend`:
+For instructions on writing and installing your own custom credential plugin, see: https://github.com/ansible/awx-custom-credential-plugin-example
-
-```python
-import collections
-
-CredentialPlugin = collections.namedtuple('CredentialPlugin', ['name', 'inputs', 'backend'])
-
-def some_callable(value_from_awx, **kwargs):
-    return some_libary.get_secret_key(
-        url=kwargs['url'],
-        token=kwargs['token'],
-        key=kwargs['secret_key']
-    )
-
-some_fancy_plugin = CredentialPlugin(
-    'My Plugin Name',
-    # inputs will be used to create a new CredentialType() instance
-    #
-    # inputs.fields represents fields the user will specify *when they create*
-    # a credential of this type; they generally represent fields
-    # used for authentication (URL to the credential management system, any
-    # fields necessary for authentication, such as an OAuth2.0 token, or
-    # a username and password). They're the types of values you set up _once_
-    # in AWX
-    #
-    # inputs.metadata represents values the user will specify *every time
-    # they link two credentials together*
-    # this is generally _pathing_ information about _where_ in the external
-    # management system you can find the value you care about i.e.,
-    #
-    # "I would like Machine Credential A to retrieve its username using
-    # Credential-O-Matic B at secret_key=some_key"
-    inputs={
-        'fields': [{
-            'id': 'url',
-            'label': 'Server URL',
-            'type': 'string',
-        }, {
-            'id': 'token',
-            'label': 'Authentication Token',
-            'type': 'string',
-            'secret': True,
-        }],
-        'metadata': [{
-            'id': 'secret_key',
-            'label': 'Secret Key',
-            'type': 'string',
-            'help_text': 'The value of the key in My Credential System to fetch.'
-        }],
-        'required': ['url', 'token', 'secret_key'],
-    },
-    # backend is a callable function which will be passed all of the values
-    # defined in `inputs`; this function is responsible for taking the arguments,
-    # interacting with the third party credential management system in question
-    # using Python code, and returning the value from the third party
-    # credential management system
-    backend = some_callable
-```
-
-Plugins are registered by specifying an entry point in the `setuptools.setup()`
-call (generally in the package's `setup.py` file - https://github.com/ansible/awx/blob/devel/setup.py):
-
-```python
-setuptools.setup(
-    ...,
-    entry_points = {
-        ...,
-        'awx.credential_plugins': [
-            'fancy_plugin = awx.main.credential_plugins.fancy:some_fancy_plugin',
-        ]
-    }
-)
-```
 
 Programmatic Secret Fetching
 ----------------------------