minor: update README before bump

Author: TylerBrock

README.md

@@ -3,7 +3,7 @@ Welcome to the MongoDB C++ Driver!
 
 Please see our [wiki page](https://github.com/mongodb/mongo-cxx-driver/wiki/Download%20and%20Compile) for information about building, testing, and using the driver.
 
-  Version [1.0.0-rc1](https://github.com/mongodb/mongo-cxx-driver/releases/tag/legacy-1.0.0-rc1)
+  Version [1.0.0-rc2](https://github.com/mongodb/mongo-cxx-driver/releases/tag/legacy-1.0.0-rc2)
   of the C++ legacy driver has been released. Help us test it out!
   Please report any bugs or issues in the C++
   [JIRA project](http://jira.mongodb.org/browse/CXX).