fixed doc for sigh - thanks @Kerndog73

docs/md/signal.md

@@ -228,38 +228,48 @@ To collect data, the `collect` member function should be used instead. Below is
 a minimal example to show how to use it:
 
 ```cpp
-struct my_collector {
-    std::vector<int> vec{};
-
-    bool operator()(int v) noexcept {
-        vec.push_back(v);
-        return true;
-    }
-};
-
 int f() { return 0; }
 int g() { return 1; }
 
 // ...
 
-entt::sigh<int(), my_collector<int>> signal;
-entt::sink sink{sigh};
+entt::sigh<int()> signal;
+entt::sink sink{signal};
 
 sink.connect<&f>();
 sink.connect<&g>();
 
 std::vector<int> vec{};
-my_collector collector = signal.collect([&vec](int value) { vec.push_back(value); });
+signal.collect([&vec](int value) { vec.push_back(value); });
 
-assert(collector.vec[0] == 0);
-assert(collector.vec[1] == 1);
+assert(vec[0] == 0);
+assert(vec[1] == 1);
 ```
 
 A collector must expose a function operator that accepts as an argument a type
 to which the return type of the listeners can be converted. Moreover, it can
 optionally return a boolean value that is true to stop collecting data, false
 otherwise. This way one can avoid calling all the listeners in case it isn't
-necessary.
+necessary.<br/>
+Functors can also be used in place of a lambda. Since the collector is copied
+when invoking the `collect` member function, `std::ref` is the way to go in this
+case:
+
+```cpp
+struct my_collector {
+    std::vector<int> vec{};
+
+    bool operator()(int v) noexcept {
+        vec.push_back(v);
+        return true;
+    }
+};
+
+// ...
+
+my_collector collector;
+signal.collect(std::ref(collector));
+```
 
 # Event dispatcher