Add credit for developer of MSDF technique (#468)

Author: toji

sample/textRenderingMsdf/meta.ts

@@ -5,7 +5,8 @@ fonts are more complex to implement than using Canvas 2D to generate text, but t
 text looks smoother while using less memory than the Canvas 2D approach, especially at high
 zoom levels. They can be used to render larger amounts of text efficiently.
 
-The font texture is generated using [Don McCurdy's MSDF font generation tool](https://msdf-bmfont.donmccurdy.com/)`,
+The font texture is generated using [Don McCurdy's MSDF font generation tool](https://msdf-bmfont.donmccurdy.com/),
+which is built on [Viktor Chlumský's msdfgen library](https://github.com/Chlumsky/msdfgen).`,
   filename: __DIRNAME__,
   sources: [
     { path: 'main.ts' },