[Issue-1966] Added Source "Stadt Mainhausen" (#1967)

* added yaml config for city Mainhausen

* updated links in README and info

---------

Co-authored-by: Steffen Meiselbach <smeiselbach@solteccon.de>
Co-authored-by: 5ila5 <38183212+5ila5@users.noreply.github.com>

doc/ics/stadt_mainhausen_de.md

@@ -0,0 +1,40 @@
+# Stadt Mainhausen
+
+Stadt Mainhausen is supported by the generic [ICS](/doc/source/ics.md) source. For all available configuration options, please refer to the source description.
+
+
+## How to get the configuration arguments
+
+- Goto <https://www.mainhausen.de/download-muellkalender> and select your street name.  
+- Right-click on `Download Kalenderdatei nur Bezirke mit *selected street name*` and copy link address.
+- Replace the `url` in the example configuration with this link.
+
+## Examples
+
+### Breslauer Straße
+
+```yaml
+waste_collection_schedule:
+  sources:
+    - name: ics
+      args:
+        url: https://www.mainhausen.de/municipal/subscribe/trash/15
+```
+### Aussiger Straße
+
+```yaml
+waste_collection_schedule:
+  sources:
+    - name: ics
+      args:
+        url: https://www.mainhausen.de/municipal/subscribe/trash/9
+```
+### Mainflinger Straße
+
+```yaml
+waste_collection_schedule:
+  sources:
+    - name: ics
+      args:
+        url: https://www.mainhausen.de/municipal/subscribe/trash/44
+```