Add suggestion to use base2

[Christewart]

As discussed in #119 we think base2 is probably the best base to use for oracles. We talked about deprecating all other bases in favor of base2.

@Tibo-lg suggested we hold off on deprecating other bases, for now in case we figure out some useful application.

I proposed we add a note for new developers that we are thinking about deprecating other bases, and maybe they can save on implementation time by just thinking in base 2.

@Tibo-lg had another good point though it may be the easiest just to implement arbitrary bases to start if you are a new developer.

At the end of the day I think we should try to be transparent with where our thinking is currently, and then let the developer make the decision on what they want to implement

[Tibo-lg]

@Christewart I think this is now covered? https://github.com/discreetlogcontracts/dlcspecs/blob/master/NumericOutcomeCompression.md#counting-adaptor-signatures