📝 clarify custom post_process docs

docs/middleware/custom_middleware.md

@@ -57,7 +57,7 @@ Unlike `process_request`, returning a value here doesn't change anything. We're
 
 This is a helper function that is available for you to override; it's not often used by middleware, but there are some ([like the pydantic middleware](middleware/pydantic.md)) that call `on_error` when there is a validation failure.
 
-## post_process(self, request: Request, response: HttpResponse, rendered_response: str) -> str:
+## post_process(self, request: Request, response: HttpResponse, rendered_response: str) -> str | bytes:
 
 > New in 1.3.0!
 
@@ -67,7 +67,7 @@ There are three things passed to `post_process`:
 
 - `request`: the request object. It's provided here purely for reference purposes; while you can technically change it here, it won't have any effect on the response.
 - `response`: the response object. The full HTML of the response has already been rendered, but the headers can still be modified here. This object can be modified in place, like in `process_response`.
-- `rendered_response`: the full HTML of the response as a string. This is the final output that will be sent to the client. Every instance of `post_process` must return the full HTML of the response, so if you want to make changes, you'll need to return the modified string.
+- `rendered_response`: the full HTML of the response as a string or bytes. This is the final output that will be sent to the client. Every instance of `post_process` must return the full HTML of the response, so if you want to make changes, you'll need to return the modified string. A string is _strongly_ preferred, but bytes are also acceptable; keep in mind that you'll be making things harder for any `post_process` middleware that comes after you.
 
 Note that this function *must* return the full HTML of the response (provided at the start as `rendered_response`. Each invocation of `post_process` overwrites the entire output of the response, so make sure to return everything that you want to send. For example, here's a middleware that ~~breaks~~ adjusts the capitalization of the response and also demonstrates passing variables into the middleware and modifies the headers with the type of transformation:
 
@@ -75,13 +75,13 @@ Note that this function *must* return the full HTML of the response (provided at
 import random
 
 from spiderweb.request import Request
+from spiderweb.response import HttpResponse
 from spiderweb.middleware import SpiderwebMiddleware
 from spiderweb.exceptions import ConfigError
 
 
 class CaseTransformMiddleware(SpiderwebMiddleware):
-    # this breaks everything, but it's hilarious so it's worth it.
-    # Blame Sam.
+    # this breaks everything, but it's hilarious so it's worth it. Blame Sam.
     def post_process(self, request: Request, response: HttpResponse, rendered_response: str) -> str:
         valid_options = ["spongebob", "random"]
         # grab the value from the extra data passed into the server object
@@ -109,6 +109,7 @@ class CaseTransformMiddleware(SpiderwebMiddleware):
             )
 
 # usage:
+from spiderweb import SpiderwebRouter
 
 app = SpiderwebRouter(
     middleware=["CaseTransformMiddleware"],