Add example to README

README.md

@@ -6,14 +6,39 @@
 ```sh
 gleam add personnummer
 ```
+
 ```gleam
 import personnummer
 
 pub fn main() {
-  // TODO: An example of the project in use
+  let assert Ok(pnr) = personnummer.new("19900101-0017")
+  io.debug(
+    [
+      "The person with personal identity number ",
+      pnr
+        |> personnummer.format(True),
+      " is a ",
+      case
+        pnr
+        |> personnummer.is_male()
+      {
+        True -> "male"
+        False -> "female"
+      },
+      " of age ",
+      pnr
+        |> personnummer.age
+        |> int.to_string(),
+    ]
+    |> string.concat,
+  )
 }
 ```
 
+```sh
+"The person with personal identity number 19900101-0017 is a male of age 34"
+```
+
 Further documentation can be found at <https://hexdocs.pm/personnummer>.
 
 ## Development