Add macOS instruction

diff --git a/plugins/chksum b/plugins/chksum
index 318f1c8b346febf427039d0455af09be2c92b1d9..06da799502038d0a88fa93561de34d488640c6fc 100755 (executable)
--- a/plugins/chksum
+++ b/plugins/chksum
@@ -2,6 +2,8 @@
 
 # Description: Create and verify checksums
 #
+# Note:  On macOS, install the relevant checksum packages from Homebrew.
+#
 # Details:
 #   - selection: it will generate one file with the checksums and filenames
 #                (and with paths if they are in another directory)