Add fromString example

Author: sharkdp

README.md

@@ -1,7 +1,7 @@
 # purescript-numbers
 Functions for working with PureScript's builtin `Number` type.
 
-## Example
+## Examples
 
 ``` purs
 > 0.1 + 0.2 == 0.3
@@ -10,4 +10,7 @@ false
 > import Data.Number
 > 0.1 + 0.2 ≅ 0.3
 true
+
+> fromString "12.34"
+(Just 12.34)
 ```