docs(@angular/cli): format [collection:schematic] as code in generate help

Wrap `[collection:schematic]` in backticks in the `ng generate` positional argument description so that it renders as inline code rather than an unresolved Markdown link reference in generated documentation.

Author: alan-agius4

packages/angular/cli/src/commands/generate/cli.ts

@@ -46,7 +46,7 @@ export default class GenerateCommandModule
       builder: (localYargs) =>
         localYargs
           .positional('schematic', {
-            describe: 'The [collection:schematic] to run.',
+            describe: 'The `[collection:schematic]` to run.',
             type: 'string',
             demandOption: true,
           })