readme: bolder claim about lack of support in IE.
readme: bolder claim about lack of support in IE.

Readme was explicitly informing about code being tested in some browsers and implicitly that is working properly.
Explicit information about known lack of IE support is placed in the end of next *.md file, so somewhat hidden.
I'm placing it in readme file linked to "Limitations" doc.
cburgmer/rasterizeHTML.js,cburgmer/rasterizeHTML.js