docs: --embed-resources flag is not covered in Distribution Overview

[salehahmed99]

Description

The Distribution Overview page does not document the --embed-resources flag available in neu build, which allows developers to bundle resources.neu directly into the binary executable, producing a single self-contained file per platform instead of the typical binary + resources.neu pair.

The current documentation only describes the two-file distribution model:

"As the first step for packaging, you can pick two files for each targeted operating system: application binary and the resource file."

This is misleading for developers as it implies two files are always required.

Proposed solution

Add a dedicated section (or a note under "Selecting files for packaging") that documents:

1. What --embed-resources does: injects resources.neu into the binary using postject, so the app ships as a single executable file with no external resource file dependency.

2. How to use it:

   neu build --embed-resources

3. The resulting distribution difference:

   Flag	Distribution output
   neu build (default)	myapp-linux_x64 + resources.neu
   neu build --embed-resources	myapp-linux_x64 (resources embedded)

4. Trade-offs: embedding makes patching/updating resources without rebuilding the binary impossible, but simplifies distribution significantly.