Explain deprecation of the 'build zone data' tool

[scw]

From Pat:

i did notice that there is no longer a tool to build zone data / classification dictionary... the classify tool help mentions this but it is a bit buried in the parameter explanations; it may be good to bring the matter of dictionary creation forward a bit.

For users of the prior releases of BTM, this can be confusing: they used to have an intergrated authoring environment, but now need to use an external version. Clarify this, in conjunction with the XLS support (#21).