Fixed question number 7 grammar

Refined the grammar of the components definition.

Author: VasileDurlesteanu

README.md

@@ -393,7 +393,7 @@ You can download the PDF and Epub version of this repository from the latest run
   **[⬆ Back to Top](#table-of-contents)**
 
 7. ### What are components?
-    Components are the most basic UI building block of an Angular app which formed a tree of Angular components. These components are subset of directives. Unlike directives, components always have a template and only one component can be instantiated per an element in a template.
+    Components are the most basic UI building block of an Angular app, which form a tree of Angular components. These components are a subset of directives. Unlike directives, components always have a template, and only one component can be instantiated per element in a template.
     Let's see a simple example of Angular component
     ```typescript
     import { Component } from '@angular/core';