renamed introduction to tutorial

docs/guide/devtools.md

@@ -27,7 +27,7 @@ textual run my_app.py
 
 The `run` sub-command assumes you have an App instance called `app` in the global scope of your Python file. If the application is called something different, you can specify it with a colon following the filename:
 
-```
+```bash
 textual run my_app.py:alternative_app
 ```
 
@@ -35,9 +35,22 @@ textual run my_app.py:alternative_app
 
     If the Python file contains a call to app.run() then you can launch the file as you normally would any other Python program. Running your app via `textual run` will give you access to a few Textual features such as live editing of CSS files.
 
+
+## Live editing
+
+If you combine the `run` command with the `--dev` switch your app will run in *development mode*.
+
+```bash
+textual run --dev my_app.py
+```
+
+One of the the features of *dev* mode is live editing of CSS files: any changes to your CSS will be reflected in the terminal a few milliseconds later.
+
+This is a great feature for iterating on your app's look and feel. Open the CSS in your editor and have your app running in a terminal. Edits to your CSS will appear almost immediately after you save. 
+
 ## Console
 
-When running a terminal application, you will generally no longer be able to use `print` when debugging (or log to the console). This is because anything you write to standard output would overwrite application content, making it unreadable. Fortunately Textual supplies a debug console of its own which has some super helpful features.
+When building a typical terminal application you are generally unable to use `print` when debugging (or log to the console). This is because anything you write to standard output will overwrite application content. Textual has a solution to this in the form of a debug console which restores `print` and adds a few additional features to help you debug.
 
 To use the console, open up **two** terminal emulators. Run the following in one of the terminals:
 
@@ -58,6 +71,7 @@ textual run --dev my_app.py
 
 Anything you `print` from your application will be displayed in the console window. Textual will also write log messages to this window which may be helpful when debugging your application.
 
+
 ### Verbosity
 
 Textual writes log messages to inform you about certain events, such as when the user presses a key or clicks on the terminal. To avoid swamping you with too much information, some events are marked as "verbose" and will be excluded from the logs. If you want to see these log messages, you can add the `-v` switch.
@@ -91,7 +105,7 @@ log("[bold red]DANGER![/] We're having too much fun")
 
 ### Log method
 
-There's a convenient shortcut to `log` available on the App and Widget objects you can use in event handlers:
+There's a convenient shortcut to `log` available on the App and Widget objects. This is useful in event handlers. Here's an example:
 
 ```python
 from textual.app import App