Update introduction.rst (#1579)

Fixed a spelling mistake. I changed deicsions to decisions.

docs/introduction/introduction.rst

@@ -51,7 +51,7 @@ Name                         Description
                              modules.  With these signals `Decision Generator` will generate the target
                              trading decisions(i.e. portfolio, orders)
                              If RL-based Strategies are adopted, the `Policy` is learned in a end-to-end way,
-                             the trading deicsions are generated directly.
+                             the trading decisions are generated directly.
                              Decisions will be executed by `Execution Env`
                              (i.e. the trading market).  There may be multiple levels of `Strategy`
                              and `Executor` (e.g. an *order executor trading strategy and intraday order executor*