Create Transactions_API.md

Author: rdeioris

docs/Transactions_API.md

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+The Trasaction API
+=
+
+Transactions in Unreal Engine 4 are sequences of recorded editor commands that can be re-executed or reverted. It is the base of the undo/redo system of Unreal Engine 4. 
+
+If you want to check how transactions are managed, open select the  "Edit->Undo History" menu item.
+
+Managing transactions
+-
+
+It is highly suggested to execute the commands with the "Undo History" panel opened:
+
+```python
+from unreal_engine.classes import Actor, Character
+import unreal_engine as ue
+
+world = ue.get_editor_world()
+
+ue.begin_transaction('My first transaction')
+actor1 = world.actor_spawn(Actor)
+actor2 = world.actor_spawn(Actor)
+actor3 = world.actor_spawn(Actor)
+ue.end_transaction()
+
+ue.begin_transaction('My second transaction')
+character1 = world.actor_spawn(Character)
+character2 = world.actor_spawn(Character)
+character3 = world.actor_spawn(Character)
+ue.end_transaction()
+
+# undo the two transactions
+ue.editor_undo()
+ue.editor_undo()
+```