Add a note about the fixed memory leak

source/release/note/2.6.0.rst

@@ -13,6 +13,7 @@ SDF
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 - The Java version of sdf2table is now slightly faster and takes up less peak memory due to improvements in writing away the parsetable to file. 
+- The old (Aster based) version of make-permissive (to add error recovery to your grammar) used to be called in a way that create a small memory leak, which would compound over time with subsequent builds. This is has now been fixed. The old version of make-permissive is only in effect if you use `sdf2table: c` in your `metaborg.yaml` file.
 
 Parser
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