added a README with API ideas

Author: geelen

README.md

@@ -0,0 +1,33 @@
+# CSS Module Loader Core
+> A loader-agnostic CSS Modules implementation, based on PostCSS
+
+## API
+
+### core.load( sourceString , pathFetcher ) => { injectableSource, exportTokens }
+
+Processes the input CSS `sourceString`, looking for dependencies such as `@import` or `:import`. When dependencies are found, it will ask the `pathFetcher` for each dependency, resolve & inline any imports, and return the following object:
+
+- `injectableSource`: the final, merged CSS file without `@import` or `:import` statements
+- `exportTokens`: the mapping from local name to scoped name, as described in the file's `:export` block
+
+These should map nicely to what your build-tool-specific loader needs to do its job.
+
+### core.plugins = pluginArray
+
+The default set of plugins is [[postcss-modules-local-by-default](https://github.com/css-modules/postcss-modules-local-by-default), [postcss-modules-extract-imports](https://github.com/css-modules/postcss-modules-extract-imports), [postcss-modules-scope](https://github.com/css-modules/postcss-modules-scope)] (i.e. the CSS Modules specification). This can override which PostCSS plugins you wish to execute, e.g.
+
+```js
+import core from 'css-loader-core'
+import autoprefixer from 'autoprefixer'
+import colorFunctions from 'postcss-color-function'
+
+// Don't run local-by-default, but use colorFunctions 
+// beforehand and autoprefixer afterwards:
+core.plugins = [
+  colorFunctions, 
+  core.plugins.extractImports, 
+  core.plugins.scope, 
+  autoprefixer("Last 2 Versions")
+]
+```
+