docs: use correct packageNames description

Author: mikael-andersson91

README.md

@@ -75,4 +75,4 @@ The scenario illustrated below shows how one can work with providing specific pr
 |Name|Description|
 |:--|:--|
 |**packagesPath**|Path to the folder containing the .nupkg packages generated by this action|
-|**packageNames**|Comma-separated list of generated package file names|
+|**packageNames**|JSON array of generated package names, for use with fromJson() in subsequent matrix jobs|