Add examples to documentation

Author: tw0po1nt

gitbook/option/sequenceAsync.md

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+## Option.sequenceAsync
+
+Namespace: `FsToolkit.ErrorHandling`
+
+Function Signature:
+
+```fsharp
+Async<'a> option -> Async<'a option>
+```
+
+Note that `sequence` is the same as `traverse id`. See also [Option.traverseAsyc](traverseAsync.md).
+
+See also Scott Wlaschin's [Understanding traverse and sequence](https://fsharpforfunandprofit.com/posts/elevated-world-4/).
+
+## Examples
+
+### Example 1
+
+```fsharp
+let a1 : Async<int option> =
+  sequenceResult (Some (Async.singleton 42))
+// async { return Some 42 }
+
+let a2 : Async<int option> =
+  sequenceAsync None
+// async { return None }
+```

gitbook/option/traverseAsync.md

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+## Option.traverseResult
+
+Namespace: `FsToolkit.ErrorHandling`
+
+Function Signature:
+
+```fsharp
+('a -> Async<'b>) -> 'a option -> Async<'b option>
+```
+
+Note that `traverse` is the same as `map >> sequence`. See also [Option.sequenceAsync](sequenceAsync.md).
+
+See also Scott Wlaschin's [Understanding traverse and sequence](https://fsharpforfunandprofit.com/posts/elevated-world-4/).
+
+## Examples
+
+### Example 1
+
+Let's assume we have a type `Customer`:
+
+```fsharp
+type Customer = {
+  Id : int
+  Email : string
+}
+```
+
+And we have a function called `getCustomerByEmail` that retrieves a `Customer` by email address asynchronously from some external source -- a database, a web service, etc:
+
+```fsharp
+// string -> Async<Customer>
+let getCustomerByEmail email : Async<Customer> = async {
+    return { Id = 1; Email = "[email protected]" } // return a constant for simplicity
+}
+```
+
+If we have a value of type `string option` and want to call the `getCustomerByEmail` function, we can achieve it using the `traverseAsync` function as below:
+
+```fsharp
+Some "[email protected]" |> Option.traverseAsync getCustomerByEmail
+// async { return Some { Id = 1; Email = "[email protected]" } }
+
+None |> Option.traverseResult tryParseInt
+// async { return None }
+```