Minor typo in seq-let info docs

[raman@google.com]

This sentence re seq-let is hard to parse -- suspect an extra "in":

<cite>
-- Macro: seq-let arguments sequence body…
     This macro binds the variables in defined in the sequence ARGUMENTS
     to the elements of the sequence SEQUENCE.  ARGUMENTS can itself
     include sequences allowing for nested destructuring.

-- 

</cite> 

In addition, the somewhat self-referential nature of the opening
sentence makes it confusing reading. That I am listening to it likely
makes it harder -- adding some quoting in addition to case changes
would make it easier reading.

<rewrite>
-- Macro: seq-let arguments sequence body…
     This macro binds the variables  listed in  `ARGUMENTS'
     to the elements of the sequence SEQUENCE.  `ARGUMENTS' can itself
     include sequences allowing for nested destructuring.

--