Fix some spelling errors

routes/categories.js

@@ -2,7 +2,7 @@ const express = require('express')
 const { catchErrors } = require('../handlers/errorHandlers')
 const router = express.Router()
 
-/* GET courses listing. */
+/* GET category listing. */
 router.get('/', catchErrors(async function (req, res, next) {
   res.render('categories', { title: 'Categories' })
 }))

routes/courses.js

@@ -13,9 +13,9 @@ router.get('/', catchErrors(async function (req, res, next) {
   res.render('courses', { title: `All Courses (${courses.length})`, categories, courses })
 }))
 
-/* GET courses listing. */
+/* GET courses listing by category. */
 router.get('/categories/:category', catchErrors(async function (req, res, next) {
-  // we get all the entries with the content type `course`
+  // we get all the entries with the content type `course` filtered by a category
   let courses = []
   let categories = []
   let activeCategory = ''