Provide a readme for running on mac osx with RStudio

macosx.md

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+# Running on Mac OSX with RStudio
+
+Currently the embedded application is windows only.
+
+The application is written in R and uses the shiny web application framework.
+
+It is possible to run the application from RStudio directly on OSX.
+
+## Requirements
+
+The following are needed.
+
+- [R](https://www.r-project.org/) - the language
+- [RStudio](https://posit.co/products/open-source/rstudio/) open source edition - the R development editor/IDE
+- [XQuartx](https://www.xquartz.org/) - X Windows for mac - this is the framework that the app expects
+
+At the time of writing the versions in use were:
+
+- R: R-4.3.2-x86_64 (intel) / R-4.3.2-arm64 (apple silicon)
+- RStudio: 2023.12.0-369
+- XQuartz: 2.8.5
+
+## Installation
+
+You can either install them directly using the links above - or - if you use mac [homebrew](https://brew.sh/) then you can install using that.
+
+```shell
+brew install --cask r
+brew install --cask rstudio
+brew install --cask xquartz
+```
+
+## Application code
+
+The app code can be downloaded from the github repository download as zip using a browser (and then unzip it in Finder) - or with git:
+
+```shell
+git clone git@github.com:deepskydetail/AstroSharp.git
+```
+
+## Setup
+
+Create a working directory somewhere you want to keep the app code:
+
+Example:
+
+```shell
+mkdir R_WD
+```
+
+Copy the resources/app directory from the app download into this directory - either via Finder or directly:
+
+Example:
+
+```shell
+cp -R Downloads/AstroSharp-DualPSF/resources/app R_WD
+```
+
+Open RStudio - set the working path to R_WD (under Preferences > General > Basic > R Sessions)
+
+Restart RStudio - at this point - the app folder should appear in the tree in the RStudio window bottom right.
+
+## Dependencies
+
+Open app/appPSFBeta.R from this folder tree.
+
+A warning should appear above the code stating that some packages are required but are not installed - click the `Install` link in the warning.
+
+At the time of writing there were 58 dependencies that were installed.
+
+Once complete - in the console area of RStudio (bottom left) - run the following:
+
+```
+install.packages("remotes")
+remotes::install_github("bips-hb/neuralnet")
+```
+
+## Run the app
+
+Now all you should need to do is hit the Run App button above the code in RStudio - upload a TIFF and get editing :)