Base: Add a man page for Help

This is largely copied from the `man` man page, since the same
information applies.

Base/usr/share/man/man1/Help.md

@@ -0,0 +1,63 @@
+## Name
+
+Help
+
+## Synopsis
+
+```**sh
+$ Help
+$ Help [section] page
+$ Help search_query
+$ Help file
+```
+
+## Description
+
+`Help` is Serenity's digital manual, the GUI counterpart to `man`.
+It lets you search for and read manual pages (or "man pages").
+
+## Sections
+
+The SerenityOS manual is split into the following *sections*, or *chapters*:
+
+1. User programs
+2. System calls
+3. Libraries
+4. Special files
+5. File formats
+6. Games
+7. Miscellanea
+8. Sysadmin tools
+
+Sections are subject to change in the future.
+
+## Examples
+
+To open Help:
+```sh
+$ Help
+```
+
+To open documentation for the `echo` command:
+```sh
+$ Help echo
+```
+
+To open the documentation for the `mkdir` command:
+```sh
+$ Help 1 mkdir
+```
+Conversely, to open the documentation about the `mkdir()` syscall:
+```sh
+$ Help 2 mkdir
+```
+
+## Files
+
+`Help` looks for man pages under `/usr/share/man`. For example,
+this man page should be located at `/usr/share/man/man1/Help.md`.
+
+## See Also
+
+* [`man`(1)](man.md) To read these same man pages from the terminal
+