docs: update version matrix

Author: Roasbeef

README.md

@@ -129,6 +129,7 @@ The following table shows the supported combinations:
 
 | LiT              | LND          | Loop         | Faraday      | Pool         |
 |------------------|--------------|--------------|--------------|--------------|
+| **v0.8.4-alpha** | v0.15.5-beta | v0.20.1-beta | v0.2.8-alpha | v0.5.8-alpha |
 | **v0.8.3-alpha** | v0.15.4-beta | v0.20.1-beta | v0.2.8-alpha | v0.5.8-alpha |
 | **v0.8.2-alpha** | v0.15.3-beta | v0.20.1-beta | v0.2.8-alpha | v0.5.8-alpha |
 | **v0.8.1-alpha** | v0.15.2-beta | v0.20.1-beta | v0.2.8-alpha | v0.5.8-alpha |