clarify idea expressed in the text // Fixing 404 error (SharePoint#629)

* clarify idea expressed in the text

* prevent 404 error

* test

* prevent 404 error

Author: p8queiroz

docs/spfx/sharepoint-framework-overview.md

@@ -4,7 +4,7 @@ The SharePoint Framework (SPFx) is a page and web part model that provides full
 
 Key features of the SharePoint Framework include:
 
-* Runs in the context of the current user and connection in the browser. There are no iFrames.
+* Runs in the context of the current user and connection in the browser. There are no iFrames (no iFrames only in client-side JavaScript injection model).
 * The controls are rendered in the normal page DOM.
 * The controls are responsive and accessible by nature.
 * Enables the developer to access the lifecycle - including, in addition to **render** -  **load**, **serialize** and **deserialize**, **configuration changes**, and more.

docs/spfx/web-parts/overview-client-side-web-parts.md

@@ -4,5 +4,5 @@ SharePoint client-side web parts are controls that appear inside a SharePoint pa
 
 ## Additional resources
 
-- [Overview of the SharePoint Framework](../sharepoint-framework-overview)
-- [SharePoint Framework development tools and libraries](../tools-and-libraries)
+- [Overview of the SharePoint Framework](../sharepoint-framework-overview.md)
+- [SharePoint Framework development tools and libraries](../tools-and-libraries.md)