small grammar updates

Author: nkoenig

quick_start/tutorial.md

@@ -26,31 +26,31 @@ Let's simulate something a bit more interesting by loading a world with a pionee
 
 You may have noticed the mysterious `worlds/pioneer2dx.world` argument in the above command. This instructs gazebo to find the `pioneer2dx.world` file, and load it on start.
 
-World files are located in a versioned system directory, for example `/usr/share/gazebo-4.0` on Ubuntu.  If you have Gazebo 4.0 installed on Ubuntu, in a terminal type the following to see a complete list of worlds.
+World files are located in a versioned system directory, for example `/usr/share/gazebo-7` on Ubuntu.  If you have Gazebo 7.0 installed on Ubuntu, in a terminal type the following to see a complete list of worlds.
 
 ~~~
-ls /usr/share/gazebo-4.0/worlds
+ls /usr/share/gazebo-7/worlds
 ~~~
 
-For a Gazebo 4.0 installation on OS X using Homebrew, type the following to see a complete list of worlds.
+For a Gazebo 7.0 installation on OS X using Homebrew, type the following to see a complete list of worlds.
 
 ~~~
-ls /usr/local/share/gazebo-4.0/worlds
+ls /usr/local/share/gazebo-7/worlds
 ~~~
 
 # Client and server separation
 
-The `gazebo` command actually run two different executables for you. The
+The `gazebo` command actually runs two different executables for you. The
 first is called `gzserver`, and the second `gzclient`.
 
 The `gzserver` executable runs the physics update-loop and sensor data
-generation. This is core of Gazebo, and can be used independently of any
+generation. This is the core of Gazebo, and can be used independently of a
 graphical interface. You may see the phrase "run headless" thrown about in
 the forums. This phrase equates to running only the `gzserver`. An example
 use case would involve running `gzserver` on a cloud computer where a user
 interface is not needed.
 
-The `gzclient` executable runs the [QT](http://qt-project.org) based user
+The `gzclient` executable runs a [QT](http://qt-project.org) based user
 interface. This application provides a nice visualization of simulation, and
 convenient controls over various simulation properties.