Refine descriptions in README and extension-manifest documentation for clarity

Author: Luuk Peters

16/umbraco-cms/customizing/extending-overview/extension-registry/README.md

@@ -1,7 +1,6 @@
 ---
 description: >-
-  Almost any UI in the Backoffice is an extension. All managed by the Extension
-  Registry on the Client at Runtime. Giving you enormous flexibility.
+  Almost any UI in the Backoffice is an extension managed by the Extension Registry.
 ---
 
 # Extension Registry
@@ -14,7 +13,7 @@ You can see which extensions are registered in the backoffice by going to Settin
 All extensions are registered in the extension registry. The registry can be manipulated at any time, meaning you can add or remove extensions at runtime. You as a developer have the same possibilities as an Umbraco HQ developer, which means what HQ can do, you can do. This also means that you can change almost everything that is by default present in Umbraco. 
 
 ## [Introduction to a Extension Manifest](extension-manifest.md)
-An Extension Manifest is a declaration on what you want to register in the Umbraco backoffice. This articles handles the layout and requirements of an Extension Manifest.
+An Extension Manifest is a declaration of what you want to register in the Umbraco backoffice. This articles handles the layout and requirements of an Extension Manifest.
 
 ## [Register an extension](extension-registry.md)
 This article handles how to register an extension using an umbraco-package.json file.

16/umbraco-cms/customizing/extending-overview/extension-registry/extension-manifest.md

@@ -6,7 +6,6 @@ description: Learn about the different methods for declaring an Extension Manife
 This page explains what an Extension Manifest for a Umbraco backoffice extension is. It outlines the manifest structure, required fields, and optional features used across types.
 
 ## What is an Extension Manifest?
-This page explains what an Extension Manifest for Umbraco backoffice extensions is. It outlines the manifest structure, required fields, and optional features used across types.
 Umbraco reads the extension manifest to register the extension in the Extension Registry.
 Each extension is of a certain type and this determines the required fields of the manifest and its available capabilities.
 An Extension Manifest declares a single backoffice extension along with its configuration.