Add Windows troubleshooting section for PATH issues

Documents the workaround for Windows users who encounter
"Executable not found at 'opencode'" error due to Electron
not fully inheriting PATH environment variable.

README.md

@@ -69,3 +69,19 @@ Currently, this is work-in-progress feature with some limitations:
 
 <img src="./assets/plugin_settings.png" alt="Available plugin settings" />
 
+## Windows Troubleshooting
+
+If you see "Executable not found at 'opencode'" despite opencode being installed:
+
+1. Find your opencode.cmd path:
+   ```
+   where opencode.cmd
+   ```
+
+2. Configure the full path in plugin settings:
+   ```
+   C:\Users\{username}\AppData\Roaming\npm\opencode.cmd
+   ```
+
+This is due to Electron/Obsidian not fully inheriting PATH on Windows.
+