doc: import chapters from aptly.info

docs/Tasks.md

@@ -1,4 +1,8 @@
 # Background Tasks
 <div>
+An aptly task is a sequence of multiple aptly commands run within a single aptly thread.
 
+For example, a task could be to [create a new repository](/doc/aptly/repo/create), [add packages to it](/doc/aptly/repo/add), [create a snapshot](/doc/aptly/snapshot/create) and [serve it](/doc/aptly/serve).
+
+Four commands can be now run in a single command.
 </div>