Fix Grammar and Spelling in gtk4-samples.rst (#78)

Author: AlleyCH

source/tutorials/gui-programming/gtk4-samples.rst

@@ -3,7 +3,7 @@ GTK4 Samples
 
 .. important::
 
-   GTK 4 is required is required to compile and run the Vala code samples.
+   GTK 4 is required to compile and run the Vala code samples.
    Depending on your environment, you may need to install a gtk4 development package.
 
    You can learn more about GTK and how to install GTK 4 at https://gtk.org
@@ -14,15 +14,15 @@ Introduction
 
 This tutorial is a subset of GTK4 Samples written in Vala.
 
-This serves as an introduction to developing GTK4 Appliations in Vala.
+This serves as an introduction to developing GTK4 Applications in Vala.
 
 Source Code
 -----------
 
-You can view the full set of Vala GTK4 Samples in in the
+You can view the full set of Vala GTK4 Samples in the
 `Vala GTK4 Samples source code repository <https://github.com/vala-lang/gtk4-samples>`_
 
-The repository includes the sample code featured in this website.
+The repository includes the sample code featured on this website.
 
 Samples
 -------
@@ -40,4 +40,4 @@ Samples
    gtk4-samples/column-view
    gtk4-samples/clipboard
    gtk4-samples/entry-completion-two-cells
-   
+