docs: clarify meaning of Incompatible VM compatibility

Co-authored-by: Ashley Cliff <[email protected]>

Author: dsloanm

reference/compatibility-matrix.md

@@ -7,7 +7,7 @@ The compatibility key:
 
 * <span style="color:green">&#x2714; Compatible</span>: Fully compatible with all Charmed HPC features. No known issues.
 * <span style="color:orange">&#x25B3; Partial</span>: May be compatible with a subset of Charmed HPC features or may have issues that require work-arounds.
-* <span style="color:red">&#x2718; Incompatible</span>: Has issues that prevent even basic use.
+* <span style="color:red">&#x2718; Incompatible</span>: Has issues that prevent all use-cases.
 
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