Add docs to format function

src/sprinkle.gleam

@@ -1,6 +1,16 @@
 import gleam/string
 import gleam/list
 
+/// Replaces any placeholders in the given format_string
+/// with the values given in the data argument.
+///
+/// ## Examples
+///
+/// ```gleam
+/// format("My name is {name}!", [#("name", "Lily")])
+/// // -> "My name is Lily!"
+/// ```
+///
 pub fn format(format_string: String, data: List(#(String, String))) -> String {
   list.fold(data, format_string, fn(acc, cur) {
     string.replace(acc, each: "{" <> cur.0 <> "}", with: cur.1)