doesn't support read_only_fields in serializer

I have serializer and Django rest docs doesn't understand read_only_fields
for example:

```
class SampleSerializer(serializers.ModelSerializer):
class Meta:
model = Wallet
fields = ('id', 'name', 'owner')
read_only_fields = ('id','owner')
```

The issue names no source file or test. Start by reproducing the SampleSerializer example and tracing how serializer metadata is converted into Django REST Framework documentation; done means the generated documentation recognizes id and owner from read_only_fields as read-only.

Written by the indexing model from the issue text.