Clarified the reasons for using RVM

ruby/README.md

@@ -9,16 +9,17 @@ PREREQUISITES
 -------------
 
 This requires Ruby 2.1, as the gRPC API surface uses keyword args.
-
 If you don't have that installed locally, you can use [RVM](https://www.rvm.io/) to use Ruby 2.1 for testing without upgrading the version of Ruby on your whole system.
+RVM is also useful if you don't have the necessary privileges to update your system's Ruby.
 ```sh
-$ command curl -sSL https://rvm.io/mpapis.asc | gpg --import -
+$ # RVM installation as specified at https://rvm.io/rvm/install
+$ gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3
 $ \curl -sSL https://get.rvm.io | bash -s stable --ruby=ruby-2.1
 $
 $ # follow the instructions to ensure that your're using the latest stable version of Ruby
 $ # and that the rvm command is installed
 ```
-- Make sure your run `source $HOME/.rvm/scripts/rvm` as instructed to complete the set up of RVM
+- *N.B* Make sure your run `source $HOME/.rvm/scripts/rvm` as instructed to complete the set-up of RVM.
 
 INSTALL
 -------
@@ -28,8 +29,8 @@ INSTALL
 - *Temporary* 
   - Install the full gRPC distribution from source on your local machine
   - Build gRPC Ruby as described in [installing from source](https://github.com/grpc/grpc/blob/master/src/ruby/README.md#installing-from-source)
-  - update path: in [Gemfile](https://github.com/grpc/grpc-common/blob/master/ruby/Gemfile) to refer to src/ruby within the gRPC directory
-  - N.B: this is necessary until the gRPC ruby gem is published
+  - update `path:` in [Gemfile](https://github.com/grpc/grpc-common/blob/master/ruby/Gemfile) to refer to src/ruby within the gRPC directory
+  - N.B: these steps are necessary until the gRPC ruby gem is published
 - Use bundler to install
 ```sh
 $ # from this directory