Adds a section on 256-colors.

Closes #35.
References #44.

readme.md

@@ -186,6 +186,14 @@ if (!chalk.supportsColor) {
 - `bgCyan`
 - `bgWhite`
 
+## 256-colors
+
+Chalk does not support support anything other than the base eight colors, which
+guarantees it will work on all terminals and systems. Some terminals,
+specifically `xterm` compliant ones, will support the full range of 8-bit
+colors. For this the lower level
+[ansi-256-colors](https://github.com/jbnicolai/ansi-256-colors) package can be
+used.
 
 ## License