Added shuf notes to the knowledge base

knowledge base/shuf.md

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+# Shuf
+
+## TL;DR
+
+```shell
+# randomize the order of lines in a file and output the result
+shuf filename
+
+# only output the first 5 entries of the result
+shuf -n 5 filename
+
+# write output to another file
+shuf filename -o output_filename
+
+# generate random numbers in range 1-10:
+shuf -i 1-10
+```