Wire up the custom-repo distribution

Add repo.json at the repo root so testers can drop the raw URL
into Dalamud's Custom Plugin Repositories list and pick Hellion
Chat up like any other Dalamud plugin. The file is generated from
the in-assembly HellionChat.json plus the extra fields a Dalamud
custom-repo entry needs:

  - DownloadLinkInstall / Update / Testing point at the GitHub
    release asset for v0.1.0 (latest.zip), so refreshing the
    plugin list pulls the released ZIP rather than building from
    source.
  - IconUrl points at the raw icon.png in the repository so the
    plugin list can render the Hellion logo even before the user
    installs the plugin.
  - CategoryTags, IsHide and IsTestingExclusive use sane defaults
    for a single-track release.

README gains an Install section with the exact custom-repo URL,
the steps to add it in Dalamud and a note about disabling
upstream Chat 2 first so the layout migration runs clean.

README.md

@@ -40,6 +40,25 @@ Bootstrap (v0.1.x). Used in production on a single user's setup. Not (yet)
 submitted to the official Dalamud plugin repository — distributed as a
 custom-repo / dev-plugin while the architecture stabilises.
 
+## Install (testers)
+
+Hellion Chat is shipped via a Dalamud **custom repository** during the
+bootstrap phase. To install:
+
+1. Open Dalamud settings (`/xlsettings`) → **Experimental**.
+2. Add a new entry under **Custom Plugin Repositories**:
+   ```
+   https://raw.githubusercontent.com/JonKazama-Hellion/HellionChat/main/repo.json
+   ```
+3. Click **Save**, then back in `/xlplugins` hit **All Plugins** and refresh.
+4. **Hellion Chat** now appears in the list — install it from there.
+5. If you previously had **Chat 2** installed, disable it first. The two
+   share their database and config dir until Hellion Chat's first launch
+   migrates everything into `pluginConfigs/HellionChat/`.
+
+Updates land in the same plugin list once the maintainer pushes a new
+`v0.1.x` tag.
+
 ## Why a fork
 
 The upstream maintainer has left filtering-related issues open since 2024