Add pugixml 1.8

docs/credits_acknowledgements.rst

@@ -104,6 +104,10 @@ The following libraries and components are incorporated into RenderDoc, listed h
 
   Compresses capture files at a higher rate of compression off-line (not at capture time).
 
+* `pugixml <https://pugixml.org/>`_ - Copyright (c) 2006-2017 Arseny Kapoulkine, distributed under the MIT License.
+
+  Used for converting capture files to and from xml.
+
 Thanks
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