docs: Update the Node version support message (#2136)

Pointing them to the release notes is safer since it will accurately reflect the support for that version of node-sass

README.md

 # node-sass
 
-#### Supported Node.js versions 0.10, 0.12, 1, 2, 3, 4, 5, 6, 7 and 8.
+#### Supported Node.js versions vary by release, please consult the [releases page](https://github.com/sass/node-sass/releases)
 
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