Now that you have a layout, you'll have to link the content template (fileadmin/templates/main_1_column_with_menu.html) to the layout and indicate in which section it will be placed. The TYPO3Buddy layout has only one section, you nevertheless need to declare this explicitely in your content template. Open fileadmin/templates/main_1_column_with_menu.html and edit the file until it looks like this:
<f:layout name="main_layout" />
<f:cObject typoscriptObjectPath="lib.content_menu" />
Note that the value of the name property of the f:layout viewhelper is the same as the file name of your layout (without the extension): <f:layout name="main_layout" /> for main_layout.html.
Please note: if your using TYPO3 v10, loading your website will result in an error at this point. Just continue following the tutorial.