cat: added the append example

pages/common/cat.md

@@ -2,10 +2,14 @@
 
 > Print and concatenate files.
 
-- Print the contents of *file1* to the standard output
+- Print the contents of a file to the standard output
 
-`cat {{file1}}`
+`cat {{file}}`
 
 - Concatenate several files into the target file.
 
 `cat {{file1}} {{file2}} > {{target-file}}`
+
+- Append serveral files into the target file.
+
+`cat {{file1}} {{file2}} >> {{target-file}}`