Adding logo assets (#235)

Adding here the finalized logo. This is almost identical to the one posted on Slack, except:

  - extremely small adjustment to the arrow head, to make it perfectly centered on and orthogonal to the stroke

  - SVG was optimized to remove redundant elements (e.g. gradients). Main logo is now only 10Kb. PNGs exported at 800dpi.

Author: portsmouth

README.md

@@ -1,7 +1,14 @@
-# OpenPBR Surface
 
+
+<br>
+<p align="center">
+<img src="images/logo/openpbr-logo-glyph.svg" alt="homepage" height="80px" style="vertical-align: middle; position: relative; bottom: 3px"/>&nbsp;&nbsp;
+<img src="images/logo/openpbr-logo-text.svg"  alt="homepage" height="96px" style="vertical-align: middle; position: relative; bottom: 3px"/>
+</p>
+<br>
 <p align="center">
-<img src="images/OpenPBR_title.jpg" title="OpenPBR demonstration scene" />
+<img src="images/OpenPBR_title.jpg" title="OpenPBR demonstration scene" width="80%"/>
+<br>
 <sub><i>Shader Playground, rendered in Arnold for Maya, using OpenPBR Surface. Artwork by Nikie Monteleone.</i></sub>
 </p>
 <br>