DOC Added txn documentation.
DOC Added txn documentation.

quantopian/pyfolio,quantopian/pyfolio,raybuhr/pyfolio,r0k3/pyfolio,ChinaQuants/pyfolio,yanheven/pyfolio,dursk/pyfolio,dursk/pyfolio,yanheven/pyfolio,YihaoLu/pyfolio,femtotrader/pyfolio,chayapan/pyfolio,ChinaQuants/pyfolio,YihaoLu/pyfolio,r0k3/pyfolio,femtotrader/pyfolio,sketchytechky/pyfolio,sketchytechky/pyfolio,raybuhr/pyfolio