Add Kreisstadt Groß-Gerau as ICS source (#1114)

* Update ics.md

* Add information about Kreisstadt Groß-Gerau

* Create keisstadt_gg_de.md

* Adde explanation for configuring the GG waste schedule

* changed files to be consistant as ICS source
fixed file naming
added yaml
added comment to url retreaval
run update_docu_links.py to update (readme/info/ics).md and generate actual source md

---------

Co-authored-by: 5ila5 <5ila5@users.noreply.github.com>

doc/ics/gross_gerau_de.md

@@ -0,0 +1,22 @@
+# Kreisstadt Groß-Gerau
+
+Kreisstadt Groß-Gerau 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
+
+- Go to <https://www.gross-gerau.de/B%C3%BCrger-Service-Online-Dienste/Ver-und-Entsorgung/Abfuhrtermine-PDF-Abfallkalender/index.php> and select your street.  
+- Click on `Als Kalenderdatei (.ics) herunterladen`, select no alarm. The ICS file will be doanloaded automatically, but one can grab the source URL. (inspecting the button (F12) reveals the URL (you need to add the prefix `https://www.gross-gerau.de`))
+- Replace the `url` in the example configuration with this link.
+
+## Examples
+
+### Hagnau
+
+```yaml
+waste_collection_schedule:
+  sources:
+    - name: ics
+      args:
+        url: https://www.gross-gerau.de/output/options.php?ModID=48&call=ical&pois=3411.298&alarm=8
+```