docs: improve Whoops page explanation

Author: kenjis

user_guide_src/source/installation/troubleshooting.rst

@@ -68,10 +68,11 @@ That is a sign that you are in production mode and have hit an
 unrecoverable error, which we don't want to show to the viewer of
 the webapp, for better security.
 
-You can see the error in the debug toolbar display by setting your environment to
-"development" (in **.env**), and reloading the page.
+You can see the error in the log file. See `CodeIgniter Error Logs`_ below.
 
-Don't forget to reset the environment to "production" once you fix the problem!
+If it is not on the production server, you should set your environment to
+"development" (in **.env**). See :ref:`setting-development-mode` for the detail.
+After that, reload the page. You will see the error and the back trace.
 
 CodeIgniter Error Logs
 ----------------------

user_guide_src/source/tutorial/index.rst

@@ -53,6 +53,9 @@ Enjoy your exploration of the CodeIgniter framework.
 Getting Up and Running
 **********************
 
+Installing CodeIgnier
+=====================
+
 You can download a release manually from the site, but for this tutorial we will
 use the recommended way and install the AppStarter package through Composer.
 From your command line type the following::
@@ -62,6 +65,11 @@ From your command line type the following::
 This creates a new folder, **ci-news**, which contains your application code, with
 CodeIgniter installed in the vendor folder.
 
+.. _setting-development-mode:
+
+Setting Development Mode
+========================
+
 By default, CodeIgniter starts up in production mode. This is a safety feature
 to keep your site a bit more secure in case settings are messed up once it is live.
 So first let's fix that. Copy or rename the ``env`` file to ``.env``. Open it up.
@@ -74,6 +82,9 @@ out. So uncomment the line with ``CI_ENVIRONMENT`` on it, and change ``productio
 
     CI_ENVIRONMENT = development
 
+Running Development Server
+==========================
+
 With that out of the way it's time to view your application in a browser. You can
 serve it through any server of your choice, Apache, Nginx, etc, but CodeIgniter
 comes with a simple command that takes advantage of PHP's built-in server to get