docs: add Coder Desktop description and documentation link (#131)

Add a descriptive blurb explaining what Coder Desktop does and link to
the official documentation at coder.com. This helps users understand the
purpose and capabilities of Coder Desktop before diving into the
technical details.

Changes:
- Added explanation of Coder Desktop's core functionality (workspace
access without port-forwarding)
- Highlighted key features like Coder Connect and file synchronization
- Included direct link to official documentation at
https://coder.com/docs/user-guides/desktop

Closes #130

---------

Co-authored-by: blink-so[bot] <211532188+blink-so[bot]@users.noreply.github.com>
Co-authored-by: deansheather <[email protected]>

Author: blink-so[bot]

README.md

@@ -1,5 +1,14 @@
 # Coder Desktop for Windows
 
+Coder Desktop allows you to work on your Coder workspaces as though they're
+on your local network, with no port-forwarding required. It provides seamless
+access to your remote development environments through features like Coder
+Connect (VPN-like connectivity) and file synchronization between local and
+remote directories.
+
+Learn more about Coder Desktop in the
+[official documentation](https://coder.com/docs/user-guides/desktop).
+
 This repo contains the C# source code for Coder Desktop for Windows. You can
 download the latest version from the GitHub releases.
 
@@ -26,4 +35,4 @@ files can be found in the same directory as the files.
 
 The binary distributions of Coder Desktop for Windows have some additional
 license disclaimers that can be found in
-[scripts/files/License.txt](scripts/files/License.txt) or during installation.
+[scripts/files/License.txt](scripts/files/License.txt) or during installation.