In \crossref{joinsplit}, clarify that balance for JoinSplit transfers is enforced by the JoinSplit statement, and that there is no consensus rule to check it directly.
In \crossref{joinsplit}, clarify that balance for JoinSplit transfers is enforced by the
JoinSplit statement, and that there is no consensus rule to check it directly.

Signed-off-by: Daira Hopwood <cd7d43d5556a38ce626d53826fddc46adc597539@jacaranda.org>

zcash/zips,zcash/zips,zcash/zips,zcash/zips