docs: add spec-file-suffix option to cli usage docs

Author: hrkeni

content/cli/usages.md

@@ -84,6 +84,7 @@ $ nest g <schematic> <name> [options]
 | `--collection [collectionName]` | Specify schematics collection. Use package name of installed npm package containing schematic.<br/> Alias: `-c` |
 | `--spec`                        | Enforce spec files generation (default)                                                                         |
 | `--no-spec`                     | Disable spec files generation                                                                                   |
+| `--spec-file-suffix [suffix]`   | Specify spec file suffix.</br> Default: spec                                                                    |
 
 #### nest build