update readme

README.md

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 # haskal's advent of code 2020 solutions
 
 sharks
+
+## a guide to this repo
+
+### `(pregexp #px"([0-9]+).rkt" (list _ day))`
+
+these are the solution files for `day`. some of them have two versions, click on the history button
+to view both. the first version is the original solution i wrote, and the second version contains
+some cleanup to make the code nicer. day 1 doesn't have an original version because i didn't commit
+it. other days may not have a cleaned up version if i didn't think any cleanup needed to be done
+
+the code aims to be as efficient as needed, but prioritizes readability and conciseness. i want to
+create a good demo of using racket and its available features to solve programming problems quickly
+and cleanly
+
+### `(or "LICENSE" "COPYING")`
+
+the license is GPL 3.0 or later, including solutions and scripts
+
+### `"inputs/"`
+
+an empty folder, this is where scripts put input files
+
+### `"scripts/aoc-lib.rkt"`
+
+this is a collection of functions for interacting with the AoC server to fetch challenges, submit
+answers, get leaderboards, and track progress (in a local file called `.status.rktd`)
+
+scripts expect some environment variables to be present
+ - `AOC_SESSION`: a session token for your account. log in, then copy the `session` cookie
+ - `AOC_YEAR`: the challenge year
+ - `AOC_LEADERBOARD`: your leaderboard ID, used for plot
+
+### `"scripts/aoc.rkt"`
+
+this is included by the template and goes into every solution by default. it exports a function to
+report answers to the challenge server, and useful libraries for challenge code to use
+
+### `"scripts/countdown"`
+
+counts down to the next challenge then initializes it from a template, downloads the input file, and
+displays the challenge text in the terminal
+
+### `"scripts/get-challenge"`
+
+a CLI application for viewing challenges. takes 1 argument for day. displays somewhat styled
+challenge text to the terminal (requires 256color)
+
+### `"scripts/get-input"`
+
+downloads the input for day `n` to `inputs/n`
+
+### `"scripts/make-day"`
+
+creates a new solution file from template and downloads the input for a given day
+
+### `"scripts/plot"`
+
+plots the scores of everyone on a private leaderboard over time, defaults to displaying the plot in
+a window
+
+### `(or "scripts/plot.scrbl" "scripts/plot.css")`
+
+define a webpage (rendered with scribble) to display the plot generated by `scripts/plot`. you can
+render it with `scribble --dest <dest> --style plot.css plot.scrbl`
+
+the plot for my leaderboard is available at <https://joan.awoo.systems/aoc2020/>
+
+### `"scripts/submit-answer"`
+
+takes a day, level, and answer and submits it. returns what the server responded
+
+
+### `"scripts/template.rktrkt"`
+
+a template (in scribble) defining the solution code for a day. should be templated with the variable
+`day` specifying the day