info about files

README.md

@@ -1,6 +1,26 @@
 # awk aoc 2021
 
-got caught in the thrill of wanting to solve the puzzles fast (?)
+got caught in the thrill of wanting to solve the puzzles fast :)
+
+[advent of code 2021: awk](https://compudanzas.net/advent_of_code_2021.html)
+
+the `NUM.awk` and `NUM_2.awk` files are the original ones written under pressure. the `*_new.awk` files are improved versions written afterwards.
+
+you can see the puzzles and get the input files at [advent of code 2021](https://adventofcode.com/2021/)
+
+# run
+
+to run a program, e.g. `01.awk`:
+
+```
+awk -f 01.awk inputfile
+```
+
+if using gawk, you should be able to use compatibility/traditional mode
+
+```
+awk -c -f 01.awk inputfile
+```
 
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