Base: Add documentation for the welcome.txt format

Base/usr/share/man/man5/Welcome.md

@@ -0,0 +1,46 @@
+# Name
+Welcome - list of entries for the Welcome program
+
+# Synopsis
+`/res/welcome.txt`
+
+# Description
+Welcome's configuration file specifies the information that Welcome should show
+to new users to onboard them with the SerenityOS system. It is based on a simple
+line-by-line format.
+
+**All lines must be less than 4096 bytes in length.**
+
+# Contents
+The file consists of lines, where each line has two parts: a one-character
+specifier `$spec`, to indicate the type of line, and the remainder of the line
+`$rem`. The remainder may have a space removed from the beginning, meaning that
+you can use (for example) `* title` instead of `*title`.
+
+## Line Types
+Each line may be one of the following types:
+
+* `*` (menu item) - Finishes the previous page (if applicable) and starts a new page, identified in the menu as `$rem`.
+* `$` (icon) - Specifies the path to a PNG file to be used as the icon for the entry. The icon will always be displayed as 16x16.
+* `>` (title) - Specifies the title that will be displayed in bold above the text. The icon will be displayed to the left, if there is one.
+* `#` (comment) - Ignored.
+
+## Content
+All lines that are not one of the special types are considered content. These
+lines are merged together unless separated by a blank line.
+
+## Examples
+```
+# Create a new page 'Welcome'
+* Welcome
+# Set the icon to the Serenity ladybug
+$ /res/icons/16x16/ladybug.png
+# Set the page title to 'SerenityOS is great!'
+> SerenityOS is great!
+
+# Content goes here.
+SerenityOS is a project that was started by @awesomekling.
+Look, this will be put after that text!
+
+And this is a new paragraph! :D
+```