Updated Whitespace (markdown)

Whitespace.md

@@ -1,3 +1,30 @@
+# Add a new line at the end of a file
+
+Each PHP/CSS/HTML file must end with a new line at the end of a file.
+
+<details><summary>Example</summary><div><br>
+
+**Bad**
+
+```PHP
+{
+    // code here
+} // This is the end of the file
+```
+
+**Good**
+
+```PHP
+{
+    // code here
+}
+// This is the end of the file
+```
+
+</div></details><br>
+
+_Reference_: [`PSR2.Files.EndFileNewline`](https://github.com/squizlabs/PHP_CodeSniffer/blob/master/src/Standards/PSR2/Sniffs/Files/EndFileNewlineSniff.php)
+
 # Do not add a whitespace before a semicolon
 
 A semicolon indicates the end of a line of code. Spaces before the semicolon is unnecessary and must be removed.