minor: clarify that legacy is not production ready

Author: TylerBrock

README.md

@@ -3,30 +3,25 @@ Welcome to the MongoDB C++ Driver!
 
 Use this branch if:
 
- - You have existing code that used the driver from the server source
- and want it to continue working without modification.
+ - You need a production ready release of the C++ driver that is not under active development.
+ - You have existing code that used the driver from the server source and want it to continue working without modification.
 
 Switch to the legacy branch if:
 
- - You are using MongoDB's C++ driver for the first time.
- - You had been using 26compat (or the driver inside of the server source) and
- want to benefit from incremental improvements but have the same overall API.
+ - You are using MongoDB's C++ driver for the first time and do not mind the driver being actively worked on.
+ - You had been using 26compat (or the driver inside of the server source) and want to benefit from incremental improvements while having the same overall API.
 
-**Please Note:** As of MongoDB 2.6.0-rc1, it is no longer possible to build the
-driver from the server sources: this repository is the only approved source for
-driver builds.
-
-The master branch will contain future development work on a new driver with a
-completely new API and implementation. It is a work in progress and currently
-should not be used.
+> **Note:** As of MongoDB 2.6.0-rc1, it is no longer possible to build the driver from the server sources: this repository is the only approved source for driver builds.
 
 ## Repository Overview
 
-| Branch   | Development        | Purpose                                               |
-| -------- | ------------------ | ----------------------------------------------------- |
-| master   | Planning           | New C++ driver (work in progress)                     |
-| legacy   | Active             | Existing C++ driver with non-compatible improvements  |
-| 26compat | Maintenance Only   | Drop in replacement for users of existing C++ driver  |
+| Branch   | Stability | Development       | Purpose                                               |
+| -------- | ----------| ----------------- | ----------------------------------------------------- |
+| master   | Unstable  | Planning          | New C++ driver (work in progress)                     |
+| legacy   | Unstable  | Active            | Existing C++ driver with non-compatible improvements  |
+| 26compat | Stable    | Maintenance Only  | Drop in replacement for users of existing C++ driver  |
+
+> **WARNING:** The master branch will contain future development work on a new driver with a completely new API and implementation. It is a work in progress and currently should not be used.
 
 ## Components