Add experimental RTX 5090 (GDDR7) memory temperature support

Reads the per-module GDDR7 DRAM sensors (FBPA DQR) directly and reports
the hotspot by default; --per-module lists each of the 8 modules.
Adds a per-device decode so the existing GDDR6/6X path is unchanged.

README.md

@@ -3,6 +3,19 @@
 Reads GDDR6/GDDR6X VRAM memory temperatures from multiple supported NVIDIA GPUs found in a host Linux system.
 These findings are based on reverse engineering of the NVIDIA GPU Linux driver.
 
+### Experimental: RTX 5090 (GDDR7)
+
+Experimental support for the RTX 5090 (Blackwell / GB202, GDDR7) is included. It reads the per-module
+DRAM sensors directly and reports the hotspot (hottest module) by default:
+
+```
+sudo gddr6                # VRAM hotspot temperature
+sudo gddr6 --per-module   # each of the 8 GDDR7 modules separately
+```
+
+This is reverse-engineered and unofficial (NVIDIA does not expose memory temperature via nvidia-smi/NVML
+on this card) — treat the readings as approximate.
+
 
 ## Prerequisites
 
@@ -46,6 +59,7 @@ sudo gddr6
 ```
 
 ## Supported GPUs
+- RTX 5090 (GB202) — GDDR7, experimental (see above)
 - RTX 4090 (AD102)
 - RTX 4080 Super (AD103)
 - RTX 4080 (AD103)