extended the docs with example appending a workflow

docs/advanced.rst

@@ -173,7 +173,7 @@ will return all completed workflows that have name *The coffee workflow*. The
 empty selection means that no firework and no firework updates are selected.
 This query is started with the command:: 
 
-  lpad_-o yaml query -f query_sample_1.yaml
+  lpad_query -o yaml query -f query_sample_1.yaml
 
 If, supposed, we have one workflow with that name and it is completed the output
 is::
@@ -253,6 +253,57 @@ https://docs.mongodb.com/manual/tutorial/query-documents/
 In the examples provided in this tutorial the queries are serialized to YAML and
 to JSON.
 
+Building up a workflow as you go
+--------------------------------
+
+Very often in a research project one does not know the workflow final structure
+at the beginning. In FireWorks one can extend exiting workflows on the LaunchPad
+duting their whole lifetime, i.e. it does not matter whether the workflow has
+been just added, is running or completed. An simple example for extending a
+workflow is given in __ Exercise 4: Extending a workflow __. Here, the
+example shows how a workflow with a single Firework performing a structure
+relaxation can be exteded with a Firework performing normal mode analysis::
+
+  cd inputs
+  lpad add -c water-turbomole_relax.yaml
+  lpad get_wflows -q '{"name": "H2O normal modes - extend as you go"}'
+::
+  state: READY
+  name: H2O normal modes - extend as you go--2906
+  created_on": 2021-02-18T14:39:54.065000
+  states_list: REA
+
+  cd ../launches
+  qlaunch -q ../config/qadapter_fh2_turbomole.yaml -w ../config/fworker_fh2_turbomole.yaml singleshot
+  
+After the job has been completed:
+
+  lpad -o yaml get_wflows -q '{"name": "H2O normal modes - extend as you go"}'
+::
+  created_on: '2021-02-18T14:39:54.065000'
+  name: H2O normal modes - extend as you go--2906
+  state: COMPLETED
+  states_list: C
+
+Now you decide to perform a normal mode anaysis and reuse the relaxed structure
+from the workflow::
+
+  cd ../inputs
+  lpad append_wflow -i 2906 -f water-turbomole_freqs.yaml
+  lpad -o yaml get_wflows -q '{"name": "H2O normal modes - extend as you go"}'
+::
+  name: H2O normal modes - extend as you go--2906
+  state: RUNNING
+  states_list: C-REA
+
+  cd ../launches
+  qlaunch -q ../config/qadapter_fh2_turbomole.yaml -w ../config/fworker_fh2_turbomole.yaml singleshot
+  lpad -o yaml get_wflows -q '{"name": "H2O normal modes - extend as you go"}'
+  created_on: '2021-02-18T14:39:54.065000'
+  name: H2O normal modes - extend as you go--2906
+  state: COMPLETED
+  states_list: C-C
+
 
 Final remark
 ------------