Update source/tutorial/deploy-replica-set.txt

Fixed the requirements section to agree with the docs here:

http://docs.mongodb.org/manual/core/replication/

The requirement for a set is two or more, but the tutorial describes
three, and it led to some confusion in the community:

http://serverfault.com/questions/462780/does-a-mongodb-replica-set-require-at-least-2-or-3-members

Author: comerford

source/tutorial/deploy-replica-set.txt

@@ -27,14 +27,13 @@ deployments require no additional members or configuration.
 Requirements
 ------------
 
-A replica set requires three distinct systems so that each system can run its own instance
-of :program:`mongod`. For development systems you can run all three
-instances of the :program:`mongod` process on a local system. (e.g. a
-laptop) or within a virtual instance. For production environments, you
-should endeavor to maintain as much separation between the members as possible.  For
-example, when using VMs in Production, each member should live on
-separate host servers, served by redundant power circuits, and with
-redundant network paths.
+A replica set requires two or more distinct systems so that each system can run its own
+instance of :program:`mongod`. This tutorial will deal with a 3 member set. For
+development systems you can run all three instances of the :program:`mongod` process on a
+local system. (e.g. a laptop) or within a virtual instance. For production
+environments, you should endeavor to maintain as much separation between the members as
+possible.  For example, when using VMs in Production, each member should live on separate
+host servers, served by redundant power circuits, and with redundant network paths.
 
 Procedure
 ---------