Update reference.md: floating-point section

Clarify type inference of floating-point literals

Author: dhardy

src/doc/reference.md

@@ -366,11 +366,19 @@ A _floating-point literal_ has one of two forms:
   optionally followed by another decimal literal, with an optional _exponent_.
 * A single _decimal literal_ followed by an _exponent_.
 
-By default, a floating-point literal has a generic type, and, like integer
-literals, the type must be uniquely determined from the context. There are two valid
+Like integer literals, a floating-point literal may be followed by a
+suffix, so long as the pre-suffix part does not end with `U+002E` (`.`).
+The suffix forcibly sets the type of the literal. There are two valid
 _floating-point suffixes_, `f32` and `f64` (the 32-bit and 64-bit floating point
 types), which explicitly determine the type of the literal.
 
+The type of an _unsuffixed_ floating-point literal is determined by type
+inference. If a floating-point type can be _uniquely_ determined from the
+surrounding program context, the unsuffixed floating-point literal has that type.
+If the program context underconstrains the type, it defaults to double-precision `f64`;
+if the program context overconstrains the type, it is considered a static type
+error.
+
 Examples of floating-point literals of various forms:
 
 ```