Correct underscore-in-number documentation

No radix actually allows underscores at the beginning of a literal

src/asm/rgbasm.5

@@ -105,7 +105,7 @@ There are a number of numeric formats.
 .It Gameboy graphics Ta \` Ta 0123
 .El
 .Pp
-Underscores are also accepted in numbers, except at the beginning of decimal ones.
+Underscores are also accepted in numbers, except at the beginning of one.
 .Pp
 The "character constant" form yields the value the character maps to in the current charmap.
 For example, by default