Create MemoryManagement.md

Author: Roberto De Ioris

docs/MemoryManagement.md

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+# Managing Memory
+
+## UObject
+
+A UObject is one of the fundamental parts of Unreal Engine. It represents an engine/editor object tracked by Unreal Engine Garbage Collector.
+
+Each UObject is constantly tracked, and whenever the Garbage Collector runs (generally every 60 seconds or in very specific parts of the engine/editor loop, like when entering PIE mode)
+it checks if the UObject has still references to other UObjects, and in negative case (no references) it will be destroyed.
+
+You can trigger a Garbage Collector run from python with:
+
+```python
+import unreal_engine as ue
+ue.console_exec('obj gc')
+```
+
+## py_UEObject
+
+this is the low-level C struct representing the python mapping between a PyObject (c struct representing a python object) and a UObject.
+Whenever you create a py_UEObject (from the UE python api) another GC (related to the python plugin) will start tracking it.
+
+Whenever the UE GC runs, the UNrealEnginePython GC will run too, checking if a UObject mapped to a py_UEObject is still alive.
+
+If the UObject mapped to a python object is dead, an exception will be triggered.
+
+This is an example:
+
+```python
+import unreal_engine as ue
+
+from unreal_engine.classes import BlueprintFactory
+
+factory = BlueprintFactory()
+# run GC
+ue.console_exec('obj gc')
+# this will raise an exception as the UObject mapped to factory has been destroyed by the GC run
+print(factory)
+```
+
+By running this script you will end with something like this:
+
+```
+PyUObject is in invalid state
+Traceback (most recent call last):
+  File "<string>", line XX, in <module>
+Exception: PyUObject is in invalid state
+```