docs: clarify generateScopedName setup (#184)

Adding documentation as requested in #108 (comment)

Author: thauma9

README.md

@@ -193,7 +193,7 @@ Configure the options for the plugin within your `.babelrc` as follows:
 |`context`|`string`|Must match webpack [`context`](https://webpack.github.io/docs/configuration.html#context) configuration. [`css-loader`](https://github.com/webpack/css-loader) inherits `context` values from webpack. Other CSS module implementations might use different context resolution logic.|`process.cwd()`|
 |`exclude`|`string`|A RegExp that will exclude otherwise included files e.g., to exclude all styles from node_modules `exclude: 'node_modules'`|
 |`filetypes`|`?FiletypesConfigurationType`|Configure [postcss syntax loaders](https://github.com/postcss/postcss#syntaxes) like sugerss, LESS and SCSS and extra plugins for them. ||
-|`generateScopedName`|`?GenerateScopedNameConfigurationType`|Refer to [Generating scoped names](https://github.com/css-modules/postcss-modules#generating-scoped-names)|`[path]___[name]__[local]___[hash:base64:5]`|
+|`generateScopedName`|`?GenerateScopedNameConfigurationType`|Refer to [Generating scoped names](https://github.com/css-modules/postcss-modules#generating-scoped-names). If you use this option, make sure it matches the value of `localIdentName` in webpack config. See this [issue](https://github.com/gajus/babel-plugin-react-css-modules/issues/108#issuecomment-334351241) |`[path]___[name]__[local]___[hash:base64:5]`|
 |`removeImport`|`boolean`|Remove the matching style import. This option is used to enable server-side rendering.|`false`|
 |`webpackHotModuleReloading`|`boolean`|Enables hot reloading of CSS in webpack|`false`|
 |`handleMissingStyleName`|`"throw"`, `"warn"`, `"ignore"`|Determines what should be done for undefined CSS modules (using a `styleName` for which there is no CSS module defined).  Setting this option to `"ignore"` is equivalent to setting `errorWhenNotFound: false` in [react-css-modules](https://github.com/gajus/react-css-modules#errorwhennotfound). |`"throw"`|