automatic compression selection for tar

Using a instead of z,j,J ... makes it easy to use different compression programms

pages/common/tar.md

@@ -22,3 +22,7 @@
 - extract a bzipped archive in the current directory
 
 `tar xjf {{source.tar.bz2}}`
+
+- create a compressed archive, using archive suffix to determine the compression programm
+
+`tar caf {{target.tar.xz}} {{file1 file2 file3}}`