Missing step to be able to import after running npm link (SharePoint#5234)

* Missing step to be able to import from npm link

I noticed that I was not able to import the library module into another webpart project unless I run "gulp build" 1st. If you dont run such command, you will get a tsc error "module is not found" since there is no "lib" folder at all.

* Use single quote instead of triple one

Author: holylander

docs/spfx/library-component-tutorial.md

@@ -56,6 +56,8 @@ localization_priority: Priority
 
 ## How to consume a 3rd party SPFx library (for local testing)
 1. Run `npm link` from the root directory of library solution. In this case it would be from the **```corporate-library```** folder.
+
+1. Right after creating the symbolic link to your new spfx library component, do not forget to run at least once `gulp serve`. You need to compile your library component at least once in order to be able to import it as a module into a different project. Remember that the package.json says that `"main": "lib/index.js"`, therefore, that ___location needs to exist prior any **import** attempt.
  
 1. This will create a local npm link to the library with the name which is provided in the ```package.json```.