SONARPY-2005 update wording to exclude in in not for-loops (#4380)

rules/S1721/python/rule.adoc

@@ -1,6 +1,6 @@
 == Why is this an issue?
 
-Parentheses are not required after the ``++assert++``, ``++del++``, ``++elif++``, ``++except++``, ``++for++``, ``++if++``, ``++in++``, ``++not++``, ``++raise++``, ``++return++``, ``++while++``, and ``++yield++`` keywords, and using them unnecessarily impairs readability. They should therefore be omitted.
+Parentheses are not required after the ``++assert++``, ``++del++``, ``++elif++``, ``++except++``, ``++for++``, ``++if++``, ``++not++``, ``++raise++``, ``++return++``, ``++while++``, and ``++yield++`` keywords. Similarly, parentheses are not required after ``++in++`` in a ``++for++`` loop. Using parentheses unnecessarily impairs readability, and therefore, they should be omitted.
 
 
 === Noncompliant code example