Add comment for clarity

Author: farhatahmad

lib/bigbluebutton_api.rb

@@ -725,7 +725,7 @@ def calculate_checksum(checksum_param)
       case @algorithm
       when "sha512"
         Digest::SHA512.hexdigest(checksum_param)
-      when "sha2", "sha256", true
+      when "sha2", "sha256", true # checks true for legacy support
         Digest::SHA256.hexdigest(checksum_param)
       else
         Digest::SHA1.hexdigest(checksum_param)