Minor grammatical updates (SharePoint#617)

Author: thechriskent

docs/spfx/extensions/overview-extensions.md

@@ -1,10 +1,10 @@
 # Overview of SharePoint Framework Extensions (preview)
 
-SharePoint Framework Extensions let developers extend the user experience of SharePoint, including ways to customize more facets of the SharePoint experience, including notification areas, the toolbars of SharePoint, and the views of list data. SharePoint Framework extensions are available for testing through Office 365 Developer Tenants during preview and later cross all of the tenants, when they will GA. 
+SharePoint Framework Extensions let developers extend the user experience of SharePoint, providing ways to customize more facets of the SharePoint experience including notification areas, the toolbars of SharePoint, and the views of list data. SharePoint Framework extensions are available for testing through Office 365 Developer Tenants during preview and later across all tenants, when they reach GA. 
 
-> You can get free Office 365 Developer Tenant by subscribing to [Office 365 Developer Program](http://dev.office.com/devprogram).
+> You can get a free Office 365 Developer Tenant by subscribing to the [Office 365 Developer Program](http://dev.office.com/devprogram).
 
-SharePoint Framework Extensions add new capabilities to extend the user experience of SharePoint within modern pages and document libraries, while leveraging the familiar tools and libraries for client-side development coming from the SharePoint Framework. Specifically, SharePoint Framework includes three new Extension types:
+SharePoint Framework Extensions add new capabilities to extend the user experience of SharePoint within modern pages and document libraries, while leveraging the familiar tools and libraries for client-side development coming from the SharePoint Framework. Specifically, the SharePoint Framework includes three new Extension types:
 
 - **ApplicationCustomizers** allow developers to add script to the page, as well as access well-known HTML element placeholders and extend them with custom renderings
 - **FieldCustomizers** can be used to provide modified views to data for fields within a list
@@ -13,17 +13,17 @@ SharePoint Framework Extensions add new capabilities to extend the user experien
 In addition to plain JavaScript projects, you can build extensions alongside common scripting frameworks, such as AngularJS and React. For example, you can use React along with components from Office UI Fabric React to quickly create experiences based on the same components used in Office 365.
 
 ## Getting started
-If you have not yet installed SharePoint Framework, please have a look on following tutorial to ready for SharePoint Framework development.
+If you have not yet installed the SharePoint Framework, please have a look at the following tutorial to get ready for SharePoint Framework development:
 
 * [Setup your development environment](../set-up-your-development-environment)
 
-If you have already previously installed SharePoint Framework, please execute following command to update your Yeoman templates with the latest version.
+If you have already installed the SharePoint Framework, please execute the following command to update your Yeoman templates with the latest version:
 
 ```
 npm install -g @microsoft/generator-sharepoint
 ```
 
-Get started with the tutorials around SharePoint Framework Extension development 
+Get started with the tutorials for SharePoint Framework Extension development:
 
 * [Build your first SharePoint SharePoint Extension (Hello World part 1)](./get-started/build-a-hello-world-extension)
 
@@ -34,8 +34,8 @@ To keep track of improvements to the SharePoint Framework, including extensions
 * [@SharePoint](https://twitter.com/sharepoint) and [@OfficeDev](https://twitter.com/officedev) on Twitter
 * [Office Developer Blog](http://dev.office.com/blogs)
 
-## Provide us feedback during preview
-SharePoint Framework Extensions preview release is available to provide SharePoint engineering feedback around the planned capabilities and functionalities. Please use the following resources to start discussion with SharePoint engineering. 
+## Provide feedback during preview
+SharePoint Framework Extensions preview release is available to provide SharePoint engineering feedback around the planned capabilities and functionalities. Please use the following resources to start discussions with SharePoint engineering:
 
 - [sp-dev-docs repository issue list](https://github.com/SharePoint/sp-dev-docs/issues) - Questions, Issues and comments
 * [SharePoint StackExchange](http://sharepoint.stackexchange.com/) (please use [#spfx](http://sharepoint.stackexchange.com/tags/spfx/), [#spfx-extensions](http://sharepoint.stackexchange.com/tags/spfx-extensions/), and [#spfx-tooling](http://sharepoint.stackexchange.com/tags/spfx-tooling/) tags)