README-CoA: add first-tester install + BugSack instructions

Walk testers through cloning into a folder named VanillaGuide (the
.toc filename, not the repo name) under Interface/AddOns/, and ask
them to install BugSack + !BugGrabber so any Lua errors come back as
copy-pasteable stacks instead of vibes.

README-CoA.md

@@ -12,6 +12,32 @@ fork ports it to the Ascension 3.3.5 / Voljin client
 (`Interface: 30300`) so it can be loaded alongside the rest of the
 CoA addon set.
 
+Installing (first testers, please read)
+---------------------------------------
+
+WoW loads addons by folder name, and the folder name has to match the
+`.toc` inside it. Our repo is called `coa-vanillaguide` but the `.toc`
+is `VanillaGuide.toc`, so **clone into a folder named `VanillaGuide`**
+under your Ascension client's `Interface/AddOns/` directory:
+
+```sh
+cd <your-ascension-client>/Interface/AddOns
+git clone https://git.sub-net.at/Exiles/coa-vanillaguide.git VanillaGuide
+```
+
+Then enable **VanillaGuide** in the in-game AddOns list, log in, and
+open the guide with `/vguide`.
+
+**Before you test, please also install [BugSack][bugsack] +
+[!BugGrabber][buggrabber].** This is a code-only port — we haven't
+loaded it in-game yet, and any Lua error you hit is the fastest way
+for us to ship a second porting pass. Paste BugSack stacks into the
+Exiles Discord or open a ticket on
+`https://git.sub-net.at/Exiles/coa-vanillaguide/issues`.
+
+[bugsack]: https://www.curseforge.com/wow/addons/bugsack
+[buggrabber]: https://www.curseforge.com/wow/addons/bug-grabber
+
 What we patched
 ---------------