docs: add json5 config option

docs/configuration.md

@@ -7,7 +7,7 @@ Configuration is supported via any or all of the below:
 - Configuration file
 - Environment
 - CLI
-- `renovate.json`, `.github/renovate.json`, `.renovaterc.json`, or `.renovaterc` in target repository
+- `renovate.json`, `renovate.json5`, `.github/renovate.json`, `.github/renovate.json5`, `.renovaterc.json`, or `.renovaterc` in target repository
 - `renovate` field of `package.json` in target repository
 
 The above are listed in reverse order of preference. i.e. `package.json`