update description for WITH Recursive's CYCLE clause

https://docs.couchbase.com/server/current/n1ql/n1ql-language-reference/with-recursive.html#cycle-clause
Expr's description needs to be updated:

(Required) An identifier representing field or path representing a field/nested-field.

May be link the definition for identifier: https://docs.couchbase.com/server/7.2/n1ql/n1ql-language-reference/identifiers.html 

And for path:https://docs.couchbase.com/server/7.2/n1ql/n1ql-language-reference/select-syntax.html#path 

Also note:
in 7.6.0
Any other expression(for eg: 1+1 arithmetic expression) would be ignored

in 7.6.2
an error would be raised:

"errors": [

        {

            "code": 3307,

            "msg": "Cycle fields validation failed for with term: <with_alias> - cause: invalid cycle field expression term: (1 + 1) only identifier/path expressions are allowed"

        }

    ]