Update docs

lib/req.ex

@@ -299,6 +299,12 @@ defmodule Req do
 
     * `:plug` - if set, calls the given plug instead of making an HTTP request over the network (via [`run_plug`](`Req.Steps.run_plug/1`) step).
 
+      The plug can be one of:
+
+        * `fun(conn)` - a function plug.
+
+        * `module` or `{module, options}` - a module plug.
+
   Finch options ([`run_finch`](`Req.Steps.run_finch/1`) step)
 
     * `:finch` - the Finch pool to use. Defaults to pool automatically started by `Req`.

lib/req/steps.ex

@@ -1118,7 +1118,11 @@ defmodule Req.Steps do
 
   ## Request Options
 
-    * `:plug` - the plug to run the request against.
+    * `:plug` - the plug to run the request against. The plug can be one of:
+
+        * `fun(conn)` - a 1-arity function that accepts a `Plug.Conn` and returns it.
+
+        * `module` or `{module, options}` - a module plug
 
   ## Examples
 

lib/req/test.ex

@@ -297,8 +297,11 @@ defmodule Req.Test do
   See [module documentation](`Req.Test`) for more examples.
 
   While this function can store any `value` under `stub_name`, usually you'll want to store
-  a *plug*, that is, a function that takes a `Plug.Conn` and returns a `Plug.Conn`, a module plug,
-  or a `{module, options}` plug.
+  a *plug*, that is:
+
+    * `fun(conn)` - a function plug.
+
+    * `module` or `{module, options}` - a module plug.
 
   ## Examples