Add assets for accessibility docs (#14)

Author: reknih

NOTICE

@@ -495,6 +495,11 @@ The Creative Commons Attribution 4.0 International License applies to:
   (https://github.com/karlrupp/microprocessor-trend-data, https://ourworldindata.org/grapher/transistors-per-microprocessor)
   Years 1971-1994 deleted
 
+* "Reiher im Flug" in files/images/heron.jpg
+  Copyright 2023 Makasch1966
+  Via Wikimedia Commons
+  (https://commons.wikimedia.org/wiki/File:Reiher_im_Flug.jpg)
+
 Attribution 4.0 International
 
 =======================================================================
@@ -889,3 +894,47 @@ licenses.
 
 Creative Commons may be contacted at creativecommons.org.
 ================================================================================
+
+================================================================================
+The Data licence Germany – attribution – version 2.0 (Datenlizenz Deutschland – Namensnennung – Version 2.0) applies to:
+
+* "Bruttostromerzeugung nach Energieträgern in Deutschland ab 1990" in
+  files/images/chart-good.png, files/images/chart-bad-regular.png, and
+  files/images/chart-bad-deuteranopia.png
+  Copyright 2025, Statistisches Bundesamt (Destatis)
+  (https://www.destatis.de/DE/Themen/Branchen-Unternehmen/Energie/Erzeugung/bar-chart-race.html)
+
+Data licence Germany – attribution – version 2.0
+
+(1) Any use will be permitted provided it fulfils the requirements of this "Data
+licence Germany – attribution – Version 2.0".
+
+The data and meta-data provided may, for commercial and non-commercial use, in
+particular
+
+1. be copied, printed, presented, altered, processed and transmitted to third
+parties;
+2. be merged with own data and with the data of others and be combined to form
+new and independent datasets; 
+3. be integrated in internal and external business processes, products and
+applications in public and non-public electronic networks.
+
+(2) The user must ensure that the source note contains the following
+information:
+
+1. the name of the provider,
+2. the annotation "Data licence Germany – attribution – Version 2.0" or
+"dl-de/by-2-0" referring to the licence text available at
+www.govdata.de/dl-de/by-2-0, and
+3. a reference to the dataset (URI).
+
+This applies only if the entity keeping the data provides the pieces of
+information 1-3 for the source note.
+
+(3) Changes, editing, new designs or other amendments must be marked as such in
+the source note.
+
+ 
+
+URL: http://www.govdata.de/dl-de/by-2-0
+================================================================================

files/images/chart-bad-deuteranopia.png

@@ -99,7 +99,11 @@ files! {
     "fonts/XITSMath-Regular.otf",
     "images/bad.svg",
     "images/base14-fonts.pdf",
+    "images/chart-bad-deuteranopia.png",
+    "images/chart-bad-regular.png",
+    "images/chart-good.png",
     "images/chinese.svg",
+    "images/color-contrast.png",
     "images/cylinder.svg",
     "images/diagram.svg",
     "images/diagrams.pdf",
@@ -108,6 +112,7 @@ files! {
     "images/f2t.png",
     "images/glacier.jpg",
     "images/graph.png",
+    "images/heron.jpg",
     "images/linked.svg",
     "images/logo.svg",
     "images/matplotlib.pdf",