docs: add minimum Arto.app version requirement (v0.15.0+)

Author: lambdalisue

README.md

@@ -5,7 +5,7 @@ A Vim/Neovim plugin to open Markdown files in [Arto](https://github.com/arto-app
 ## Requirements
 
 - Vim 9.0+ or Neovim 0.10+
-- [Arto.app](https://github.com/arto-app) installed at `/Applications/Arto.app` (configurable)
+- [Arto.app](https://github.com/arto-app) v0.15.0+ installed at `/Applications/Arto.app` (configurable)
 
 ## Installation
 

doc/arto.txt

@@ -16,8 +16,8 @@ INTERFACE				|arto-interface|
 =============================================================================
 INTRODUCTION						*arto-introduction*
 
-*arto.vim* is a Vim/Neovim plugin to open Markdown files in Arto, a native
-macOS Markdown reader application.
+*arto.vim* is a Vim/Neovim plugin to open Markdown files in Arto (v0.15.0+),
+a native macOS Markdown reader application.
 
 https://github.com/arto-app