README: Add deprecation notice

Author: deathaxe

README.md

@@ -1,19 +1,52 @@
-# Less syntax for Sublime Text 3
+# Less
 
-Provides syntax highlighting for `.less` (or `.css.less`) files, with
+[Less]() syntax definitions [Sublime Text].
+
+Highlights `.less` (or `.css.less`) files, and provides
 
 - snippets
 - completions
 - symbols
 
-Highlights code using up to date specifications for properties and values to help you catch typos.
+> **Note**
+>
+> This version is no longer maintained.
+>
+> It is shipped for backward compatibility reasons and to respect the original authors efforts.
+>
+> see: https://github.com/danro/LESS-sublime
+>
+> **An up-to-date working LESS syntax definition requires ST4107+.**
 
 ## Installation
 
-This package is available through [Package Control](https://packagecontrol.io)
+### Package Control
+
+The easiest way to install is using [Package Control](https://packagecontrol.io). It's listed as `LESS`.
+
+1. Open `Command Palette` using <kbd>ctrl+shift+P</kbd> or menu item `Tools → Command Palette...`
+2. Choose `Package Control: Install Package`
+3. Find `LESS` and hit <kbd>Enter</kbd>
+
+### Manual Install
+
+1. Download appropriate [LESS.sublime-package](https://github.com/SublimeText/LESS/releases) for your Sublime Text build.  
+   _A suffix (e.g. `-st4xxx`) denotes the least required ST build for the sublime-package to work._
+2. Rename it to _LESS.sublime-package_
+3. Copy it into _Installed Packages_ directory
+
+> **Note**
+>
+> To find _Installed Packages_...
+>
+> 1. call _Menu > Preferences > Browse Packages.._
+> 2. Navigate to parent folder
 
+> **Warning**
+>
+> Manually installed packages are not automatically updated by Package Control.
 
-## Buy me a coffee 
+## Buy me a coffee
 
 ☕️👌🏻