fixes in wording and adding the digest scripts

0_D0002_18/check-sha-digests.sh

@@ -0,0 +1,5 @@
+# loop over all *.bin.DIGEST files
+
+for filename in *.bin.DIGEST; do
+    shasum -a 256 -c $filename
+done

0_D0002_18/create-sha-digests.sh

@@ -0,0 +1,8 @@
+# bash script that runs shasum on all *.bin files in this directory
+# and creates a file called $filename.DIGEST
+
+# loop over all *.bin files
+for filename in *.bin; do
+    # create a file called $filename.DIGEST
+    shasum -a 256 $filename > $filename.DIGEST
+done