expand equals section to explain value classes and difference in Float,Double

[SauravDas90]

For primitive fields whose type is not float or double, use the == operator for
comparisons; for object reference fields, invoke the equals method recursively;
for float fields, use the Float.compare method; and for double fields, use
Double.compare. The special treatment of float and double fields is made
necessary by the existence of Float.NaN, -0.0f and the analogous double
constants; see the Float.equals documentation for details. For array fields,
apply these guidelines to each element. If every element in an array field is significant,
you can use one of the Arrays.equals methods added in release 1.5.

[HugoMatilla]

Can you make a PR for this?