DOCS-11374 Clarify WT cache calculation

Author: kallimachos

source/includes/extracts-wired-tiger.yaml

@@ -172,7 +172,7 @@ content: |
    Starting in 3.4, the WiredTiger internal cache, by default, will use
    the larger of either:
 
-   - 50% of RAM minus 1 GB, or
+   - 50% of (RAM - 1 GB), or
 
    - 256 MB.
 ---