Mark ZepSense as optional in the README

README.md

@@ -1,5 +1,7 @@
 # OctoBus
 
+[![ZepSense](https://img.shields.io/badge/ZepSense-Optional-yellow.svg)](https://github.com/Phridgey/OctoBus)
+
 **OEVG fork version 1.3.6-oevg.3**, based on Phridgey’s OctoBus 1.3.6.
 
 Arrival timers for the Horde zeppelins and boats, for the vanilla 1.12.1 client (tested on WoW 1.18.1 clients).
@@ -8,7 +10,7 @@ Each row reads **start -> end**, for example `Orgrimmar -> Undercity`, with a li
 
 See the [changelog](CHANGELOG.md) for what changed in each version.
 
-OctoBus needs one extra file, `ZepSense.dll`, which you install by hand in the game folder. Your launcher can install the addon but not the DLL. See [Install](#install).
+The optional `ZepSense.dll` lets OctoBus observe live transport positions. Install it by hand in the game folder. See [Install](#install).
 
 ## Screenshots
 
@@ -68,7 +70,7 @@ Switch with a click on the window title, or `/ob all`.
 
 ## Requirements
 
-1. **`ZepSense.dll`**, a small client DLL that exposes one Lua function, `ZepTransports()`, which returns the position of every zeppelin/boat the client currently has loaded. The addon cannot see transports without it. Without the DLL, every timer is set from the server's restart time and the built-in offsets, which is close (usually within 20 seconds, marked `~`), and becomes exact as soon as a DLL user shares the current times (see Shared timers below).
+1. **Optional: `ZepSense.dll`**, a small client DLL that exposes one Lua function, `ZepTransports()`, which returns the position of every zeppelin/boat the client currently has loaded. The addon cannot see transports without it. Without the DLL, every timer is set from the server's restart time and the built-in offsets, which is close (usually within 20 seconds, marked `~`), and becomes exact as soon as a DLL user shares the current times (see Shared timers below).
 2. A client setup that loads DLLs listed in `dlls.txt`.
 
 ## Install