HPCC-10340 Document OPTIONS for Skew

Signed-off-by: JamesDeFabia <James.Defabia@LexisNexis.com>
Whilst a skew of 1.0 cannot be exceeded, so will be equivalent to disabling. 0.0 explicitly means disabled.
But more importantly, as mentioned in previous comment, it is only used if the ECL SKEW attribute is missing and then only if it is set. So it doesn't really make sense to talk about a disable value in this context.