[llvm] [Coroutines] Documentation for custom ABIs (PR #111781)

[Chuanqi Xu via llvm-commits]

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@@ -749,6 +750,65 @@ and python iterator `__next__` would look like:
     return *(int*)coro.promise(hdl, 4, false);
   }
 
+Custom ABIs and Plugin Libraries
+--------------------------------
+
+Plugin libraries can extend coroutine lowering enabling a wide variety of users
+to utilize the coroutine transformation passes. An existing coroutine lowering
+is extended by: 1. defining custom ABIs that inherit from the existing ABIs,
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ChuanqiXu9 wrote:

Let's seperate the list point. It is not easier to read it as is

https://github.com/llvm/llvm-project/pull/111781