Fix typo in EESSI documentation

Author: claudia-lola

docs/eessi.md

@@ -61,7 +61,7 @@ To find your cuda version run `nvcc --version`
 | CUDA 11.4 – 11.8     | no matching GCC module in EESSI 2023.06                             |
 | CUDA < 11.4          | not supported                                                       |
 
-To load correct ESSI module run, substituing x for the compatible GCC version: 
+To load correct ESSI module run, substituting x for the compatible GCC version: 
 ```[bash]
 module load GCC/12.x.0
 ```