doc(README.md) update including requirements section

README.md

@@ -2,6 +2,26 @@
 
 You can use wp-browser to test WordPress sites, plugins and themes.
 
+## Requirements
+
+Depending on the nature of your project, there are different requirements it will need to satisfy before getting started.
+
+### Site
+
+* Ensure you're running the `vendor/bin/codecept init wpbrowser` command from the root directory of your WordPress site.
+* Ensure the directory contains the WordPress installation files. In a standard scenario you should have extracted WordPress files in this directory.
+* Ensure your installation is configured: it should contain a `wp-config.php` file.
+
+### Plugin
+
+* Ensure you're running the `vendor/bin/codecept init wpbrowser` command from the root directory of your plugin; this should be the directory that contains the PHP file defining the [plugin header][6].
+
+### Theme
+
+* Ensure you're running the `vendor/bin/codecept init wpbrowser` command from the root directory of your theme; this should be the directory that contains the `style.css` file defining [the theme header][7].
+
+If you decide to use the quick installation, then your PHP version should have the `sqlite3` extensions installed and activated. You can check this using the `php -m` command and verifying the `sqlite3` extension is among the active extensions.
+
 ## Installation
 
 Add wp-browser to your project as a development dependency using [Composer][1]