updated README

The readme used to instruct users to edit the `installed` parameters of the images.json file, but in the latest version of PiBakery, this is no longer necessary.

Author: davidferguson

README.md

@@ -36,7 +36,7 @@ If you're on macOS it's important you run `npm run setup` the first time [to cre
 
 Then you'll need to download and extract the Raspberry Pi operating system (currently only raspbian and raspbian lite) .img files into the `os/` directory. If you're on Windows or Linux, the directory is inside the `pibakery` folder, and if you're on macOS, it's located `/Library/Application Support/PiBakery/os`. The operating systems can be downloaded in `.7z` format for the [pibakery-raspbian releases page](https://github.com/davidferguson/pibakery-raspbian/releases).
 
-Lastly you'll need to create a file `images.json` inside the `os` folder which tells PiBakery which operating systems you have installed and available for use. Download the example file from [the pibakery-raspbian repo](https://raw.githubusercontent.com/davidferguson/pibakery-raspbian/master/images.json), save it as `images.json` into the `os` folder where you stored the .img files, and then change the values of the `installed` paramater for each of the operating systems depending on which ones you have installed.
+Lastly you'll need to create a file `images.json` inside the `os` folder which tells PiBakery which operating systems you have installed and available for use. Download the example file from [the pibakery-raspbian repo](https://raw.githubusercontent.com/davidferguson/pibakery-raspbian/master/images.json) and save it as `images.json` into the `os` folder where you stored the .img files.
 
 You can then run PiBakery using
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