Add Use A Specific Config File as a webpack til

webpack/use-a-specific-config-file.md

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+# Use A Specific Config File
+
+When running `webpack`, the default config file that it looks for is
+`webpack.config.js`. If you have a project that uses different webpack
+config files for different environments, you will need to specify which
+config file webpack should use. The `--config` flag can be used with
+`webpack` to specify that file. For instance, if you want to use your
+production webpack config, run a command like the following:
+
+```
+$ webpack --config webpack.config.production.js
+```