Add a boilerplate concept for one of the tutorials

docs/introductory_tutorials/tutorial_1.rst

@@ -1,6 +1,47 @@
 .. _tutorial_1_label:
 
-First tutorial
-~~~~~~~~~~~~~~~~~~~~~~
+District heating supply optimization
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-This page will display the first basic tutorial.
+In this tutorial we will optimize the portfolio of a heating provider. balblable
+balblable
+
+.. figure:: /_files/example_network.svg
+    :align: center
+    :alt: Structure of the heating supplier's portfolio
+    :figclass: only-light
+
+    Structure of the heating supplier's portfolio
+
+.. figure:: /_files/example_network_darkmode.svg
+    :align: center
+    :alt: Structure of the heating supplier's portfolio
+    :figclass: only-dark
+
+    Structure of the heating supplier's portfolio
+
+The tutorial is set up in four steps:
+
+1. asdasd
+2. asdasd
+3. asdasd
+4. asdasdsa
+
+Step 1: Build the linear model
+------------------------------
+
+prepare the model, import stuff
+
+.. literalinclude:: /../tutorial/introductory/utilities-heat-supply.py
+    :language: python
+    :start-after: [sec_1]
+    :end-before: [sec_2]
+
+next step, we need demand data
+
+.. literalinclude:: /../tutorial/introductory/utilities-heat-supply.py
+    :language: python
+    :start-after: [sec_2]
+    :end-before: [sec_3]
+
+next step, we need demand data

tutorial/introductory/utilities-heat-supply.py

@@ -0,0 +1,5 @@
+# %%[sec_1]
+import oemof.solph as solph
+# %%[sec_2]
+import oemof.solph as solph
+# %%[sec_3]