docs: document APNG support

Author: craftablescience

README.md

@@ -219,11 +219,17 @@ Several modern C++20 libraries for sanely parsing Valve formats, rolled into one
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-    <td rowspan="23"><code>vtfpp</code></td>
+    <td rowspan="25"><code>vtfpp</code></td>
+    <td><a href="https://wiki.mozilla.org/APNG_Specification">APNG</a></td>
+    <td align="center">✅</td>
+    <td align="center">❌</td>
+    <td rowspan="25" align="center">Python</td>
+  </tr>
+  <tr><!-- empty row to disable github striped bg color --></tr>
+  <tr>
     <td><a href="https://en.wikipedia.org/wiki/BMP_file_format">BMP</a></td>
     <td align="center">✅</td>
     <td align="center">✅</td>
-    <td rowspan="23" align="center">Python</td>
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docs/index.md

@@ -191,11 +191,16 @@ Several modern C++20 libraries for sanely parsing Valve formats, rolled into one
     <td align="center">✅</td>
   </tr>
   <tr>
-    <td rowspan="12"><code>vtfpp</code></td>
+    <td rowspan="13"><code>vtfpp</code></td>
+    <td><a href="https://wiki.mozilla.org/APNG_Specification">APNG</a></td>
+    <td align="center">✅</td>
+    <td align="center">❌</td>
+    <td rowspan="13" align="center">Python</td>
+  </tr>
+  <tr>
     <td><a href="https://en.wikipedia.org/wiki/BMP_file_format">BMP</a></td>
     <td align="center">✅</td>
     <td align="center">✅</td>
-    <td rowspan="12" align="center">Python</td>
   </tr>
   <tr>
     <td><a href="https://openexr.com">EXR</a> v1</td>