Added simple example

Had some difficult figuring this one out, as this is so straight forward and is the simplest use case, maybe should be included at the top of the docs ?

USAGE.md

@@ -33,6 +33,18 @@ If using Compression Stream classes directly and you don't want the wrapped stre
 
 Also, look over the tests for more thorough [examples](https://github.com/adamhathcock/sharpcompress/tree/master/tests/SharpCompress.Test)
 
+### Create Zip Archive from multiple files
+```C#
+using(var archive = ZipArchive.Create())
+{
+    archive.AddEntry("file01.txt", "C:\\file01.txt");
+    archive.AddEntry("file02.txt", "C:\\file02.txt");
+    ...
+    
+    archive.SaveTo("C:\\temp.zip", CompressionType.Deflate);
+}
+```
+
 ### Create Zip Archive from all files in a directory to a file
 
 ```C#
@@ -143,4 +155,4 @@ foreach(var entry in tr.Entries)
 {
     Console.WriteLine($"{entry.Key}");
 }
-```
+```