Fix wording about the let command to be less confusing.
Thanks to @hoelzro on GitHub for pointing it out.
    
        | author | 
        Steve Losh <steve@stevelosh.com> | 
    
    
        | date | 
        Fri, 12 Oct 2012 19:08:59 -0400 | 
    
    
    
        | parents | 
        004078be4e90 
 | 
    
    
        | children | 
        8da4158741c9
 | 
    
    
        | branches/tags | 
        (none) | 
    
    
        | files | 
        chapters/19.markdown  | 
    
Changes
    
--- a/chapters/19.markdown	Fri Oct 12 19:05:27 2012 -0400
+++ b/chapters/19.markdown	Fri Oct 12 19:08:59 2012 -0400
@@ -56,7 +56,8 @@
 integer "0" as "false" and the integer "1" as "true".  It's reasonable to assume
 that Vim treats *any* non-zero integer as "truthy", and this is indeed the case.
 
-We can also *set* options as variables.  Run the following commands:
+We can also *set* options as variables using the `let` command.  Run the
+following commands:
 
     :::vim
     :let &textwidth = 100