Add download video and save playlist support.

README.md

@@ -1,3 +1,30 @@
 # PlaylistSaver
 
-A tool to save your youtube playlist. **VERY UNSTABLE**
+A tool to save your youtube playlist. **VERY UNSTABLE**
+
+## Development
+
+Create a virtual environment and install the project with its build tools:
+
+```powershell
+python -m venv .venv
+.\.venv\Scripts\python.exe -m pip install -e ".[build]"
+```
+
+Run from source:
+
+```powershell
+.\.venv\Scripts\playlist-saver.exe
+```
+
+## Build
+
+Build the application with PyInstaller:
+
+```powershell
+.\build.ps1 -Clean
+```
+
+The application is written to `dist\PlaylistSaver`. The build includes only the
+bundled mpv files matching the operating system and CPU architecture on which the
+build is performed. Build each target platform on that platform.