docs: add macaroon usage examples to python docs

docs/grpc/python.md

@@ -128,6 +128,51 @@ for payment in stub.SendPayment(request_iterable):
 ```
 This example will send a payment of 100 satoshis every 2 seconds.
 
+#### Using Macaroons
+
+To authenticate using macaroons you need to include the macaroon in the metadata of the request.
+
+```python
+# Lnd admin macaroon is at ~/.lnd/admin.macaroon on Linux and
+# ~/Library/Application Support/Lnd/admin.macaroon on Mac
+with open('~/.lnd/admin.macaroon', 'rb') as f:
+    macaroon_bytes = f.read()
+    macaroon = codecs.decode(macaroon_bytes, 'hex')
+```
+
+The simplest approach to use the macaroon is to include the metadata in each request as shown below.
+
+```python
+stub.GetInfo(ln.GetInfoRequest(), metadata=[('macaroon', macaroon)])
+```
+
+However, this can get tiresome to do for each request, so to avoid explicitly including the macaroon we can update the credentials to include it automatically.
+
+```python
+def metadata_callback(context, callback):
+    # for more info see grpc docs
+    callback([('macaroon', self.macaroon)], None)
+
+
+# build ssl credentials using the cert the same as before
+cert_creds = grpc.ssl_channel_credentials(cert)
+
+# now build meta data credentials
+auth_creds = grpc.metadata_call_credentials(metadata_callback)
+
+# combine the cert credentials and the macaroon auth credentials
+# such that every call is properly encrypted and authenticated
+combined_creds = grpc.composite_channel_credentials(cert_creds, auth_creds)
+
+# finally pass in the combined credentials when creating a channel
+channel = grpc.secure_channel('localhost:10009', combined_creds)
+stub = lnrpc.LightningStub(channel)
+
+# now every call will be made with the macaroon already included
+stub.GetInfo(ln.GetInfoRequest())
+```
+
+
 ### Conclusion
 
 With the above, you should have all the `lnd` related `gRPC` dependencies