Reorganize Documentation: Move ReadOlny Methods description its own section (#44947)

Author: jiabiao

docs/orleans/grains/request-scheduling.md

@@ -207,6 +207,8 @@ public interface IMyGrain : IGrainWithIntegerKey
 }
 ```
 
+The `GetCount` method doesn't modify the grain state, so it's marked with `ReadOnly`. Callers awaiting this method invocation aren't blocked by other `ReadOnly` requests to the grain, and the method returns immediately.
+
 ### Call chain reentrancy
 
 If a grain calls a method which on another grain which then calls back into the original grain, the call will result in a deadlock unless the call is reentrant. Reentrancy can be enabled on a per-call-site basis by using *call chain reentrancy*. To enable call chain reentrancy, call the <xref:Orleans.Runtime.RequestContext.AllowCallChainReentrancy> method, which returns a value that allows reentrance from any caller further down the call chain until it is disposed. This includes reentrance from the grain calling the method itself. Consider the following example:
@@ -254,8 +256,6 @@ If you were to instead prevent the deadlock by annotating the `GetDisplayName()`
 
 Call chain reentrance can also be *suppressed* using the <xref:Orleans.Runtime.RequestContext.SuppressCallChainReentrancy> method. This has limited usefulness to end developers, but it is important for internal use by libraries which extend Orleans grain functionality, such as [streaming](../streaming/index.md) and [broadcast channels](../streaming/broadcast-channel.md) to ensure that developers retain full control over when call chain reentrancy is enabled.
 
-The `GetCount` method doesn't modify the grain state, so it's marked with `ReadOnly`. Callers awaiting this method invocation aren't blocked by other `ReadOnly` requests to the grain, and the method returns immediately.
-
 ### Reentrancy using a predicate
 
 Grain classes can specify a predicate to determine interleaving on a call-by-call basis by inspecting the request. The `[MayInterleave(string methodName)]` attribute provides this functionality. The argument to the attribute is the name of a static method within the grain class that accepts an <xref:Orleans.CodeGeneration.InvokeMethodRequest> object and returns a `bool` indicating whether or not the request should be interleaved.