update README

Author: MasonProtter

README.md

@@ -5,21 +5,28 @@ StableTasks is a simple package with one main API `StableTasks.@spawn` (not expo
 It works like `Threads.@spawn`, except it is *type stable* to `fetch` from.
 
 ``` julia
-julia> Core.Compiler.return_type(() -> fetch(StableTasks.@spawn 1 + 1), Tuple{})
-Int64
+julia> using StableTasks, Test
+
+julia> @inferred fetch(StableTasks.@spawn 1 + 1)
+2
 ```
 versus
 
 ``` julia
-julia> Core.Compiler.return_type(() -> fetch(Threads.@spawn 1 + 1), Tuple{})
-Any
+julia> @inferred fetch(Threads.@spawn 1 + 1)
+ERROR: return type Int64 does not match inferred return type Any
+Stacktrace:
+ [1] error(s::String)
+   @ Base ./error.jl:35
+ [2] top-level scope
+   @ REPL[3]:1
 ```
 
 The package also provides `StableTasks.@spawnat` (not exported), which is similar to `StableTasks.@spawn` but creates a *sticky* task (it won't migrate) on a specific thread.
 
 ```julia
 julia> t = StableTasks.@spawnat 4 Threads.threadid();
 
-julia> fetch(t)
+julia> @inferred fetch(t)
 4
 ```