Add readme with mister install info

README.md

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+# Reflex Adapt
+
+## MiSTer
+
+Install the Adapt firmware updater on MiSTer by downloading [reflex_updater.sh](https://github.com/misteraddons/Reflex-Adapt/releases/latest/download/reflex_updater.sh) and copying it to the `Scripts` folder on your SD card.
+
+Alternatively, add the following to your `downloader.ini` file to install and auto-update through Downloader and Update All:
+
+```
+[misteraddons/reflexadapt]
+db_url = https://github.com/misteraddons/Reflex-Adapt/releases/latest/download/reflexadapt.json
+```
+
+The `reflex_updater.sh` script can then be launched from the Scripts menu.