Adjust bson v3 docs to reference v3 (#221)

Co-authored-by: Oleg Pudeyev <[email protected]>

Author: p-mongo

docs/tutorials/bson-v3.txt

@@ -19,23 +19,23 @@ This tutorial discusses using the core Ruby BSON gem.
 Installation
 ------------
 
-The BSON gem is hosted on `Rubygems <http://rubygems.org>`_ and can be installed
-manually or with bundler.
+The BSON library is hosted on `Rubygems <http://rubygems.org>`_ and can be
+installed manually or with bundler.
 
 To install the gem manually:
 
 .. code-block:: sh
 
-    gem install bson
+    gem install bson -v '~> 3.0'
 
-To install the gem with bundler, include the following in your Gemfile:
+To install the gem with bundler, include the following in your ``Gemfile``:
 
 .. code-block:: ruby
 
     gem 'bson', '~> 3.0'
 
-The BSON gem is compatible with MRI 1.9.3, 2.0.x, 2.1.x, 2.2.x, JRuby 1.7.x, and
-Rubinius 2.5.x
+The BSON gem is compatible with MRI 1.9.3, 2.0.x, 2.1.x, 2.2.x, JRuby 1.7.x,
+and Rubinius 2.5.x
 
 
 BSON Serialization