Add float representation info to module docs

Addresses gleam-lang#783.

src/gleam/float.gleam

@@ -1,4 +1,21 @@
 //// Functions for working with floats.
+//// 
+//// ## Float representation
+//// 
+//// Floats are represented as 64 bit floating point numbers on both the Erlang
+//// and JavaScript runtimes. The floating point behaviour is native to their
+//// respective runtimes, so their exact behaviour will be slightly different on
+//// the two runtimes. 
+//// 
+//// ### Infinity and NaN
+//// 
+//// Under the JavaScript runtime, exceeding the maximum (or minimum)
+//// representable value for a floating point value will result in Infinity (or
+//// -Infinity). Should you try to divide two infinities you will get NaN as a
+//// result. 
+//// 
+//// When running on BEAM, exceeding the maximum (or minimum) representable
+//// value for a floating point value will raise an error.
 ////
 //// ## Division by zero
 ////