docs: add build section

Author: CyanVoxel

docs/install.md

@@ -341,6 +341,22 @@ The entry point for TagStudio is `src/tagstudio/main.py`. You can target this fi
     }
     ```
 
+## Building
+
+To build your own executables of TagStudio, first follow the steps in "[Installing with PIP](#installing-with-pip)" including the developer dependencies step. Once that's complete, run the following PyInstaller command:
+
+```
+pyinstaller tagstudio.spec
+```
+
+If you're on Windows or Linux and wish to build a portable executable, then pass the following flag:
+
+```
+pyinstaller tagstudio.spec -- --portable
+```
+
+The resulting executable file(s) will be located in a new folder named "dist".
+
 ## Third-Party Dependencies
 
 For audio/video thumbnails and playback you'll also need [FFmpeg](https://ffmpeg.org/download.html) installed on your system. If you encounter any issues with this, please reference our [FFmpeg Help](./help/ffmpeg.md) guide.