broadcast doc

doc/usecases/broadcast.md

@@ -1,4 +1,31 @@
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-[!badge variant="primary" text="low level"]
+
+[!badge variant="primary" text="low level"]
+
+## Usage Example
+
+```dart
+  final myBroadcast = ndk.broadcast.broadcast(
+      nostrEvent: Nip01Event(
+        pubKey:
+            '3bf0c63fcb93463407af97a5e5ee64fa883d107ef9e558472c4eb9aaaefa459d',
+        kind: 1,
+        tags: [],
+        content: 'Hello, World!',
+      ),
+    );
+    final result = await myBroadcast.broadcastDoneFuture;
+    for (final relayResponse in result) {
+      print(
+          "broadcast on ${relayResponse.relayUrl}:  ${relayResponse.broadcastSuccessful}");
+    }
+
+```
+
+## When to use
+
+Broadcast schould be used when your usecase has no broadcasting method. \
+Signing is done automatically, and you can specify a custom signer just for one broadcast. \
+By default the inbox/outbox model is used for broadcasting looking at the event data (e.g. if its a reply) you can also specify specific relays to broadcast to.