add F# example for task-based usage (#449)

Author: baronfel

docs/mdsource/fsharp.source.md

@@ -14,6 +14,9 @@ F# does not respect implicit operator conversion. `SettingsTask` uses implicit o
 
 snippet: FsTest
 
+Tasks can also be used directly via a `task` computation expression builder, such as the ones included in [Ply](https://github.com/crowded/ply), [TaskBuilder.fs](https://github.com/rspeele/TaskBuilder.fs), or (starting with F# 6.0) FSharp.Core:
+
+snippet: FsTestTask
 
 ## Full tests
 

src/FSharpTests/Tests.MyTaskTest.verified.txt

@@ -0,0 +1 @@
+15

src/FSharpTests/Tests.fs

@@ -20,6 +20,14 @@ let MyTest () =
   }
 // end-snippet
 
+// begin-snippet: FsTestTask
+[<Fact>]
+let MyTaskTest () =
+  task {
+    do! Verifier.Verify(15)
+  }
+// end-snippet
+
 // begin-snippet: WithSettings
 [<Fact>]
 let WithFluentSetting () =