doubly-linked-list: Fix inaccurate instructions

.gitignore

@@ -7,3 +7,4 @@ tmp
 exercises/*/*/Cargo.lock
 exercises/*/*/clippy.log
 .vscode
+.prob-spec

bin/symlink_problem_specifications.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+set -eo pipefail
+
+cd "$(git rev-parse --show-toplevel)"
+
+for exercise in exercises/practice/*; do
+    name="$(basename "$exercise")"
+    if [ -d "problem-specifications/exercises/$name" ]; then
+        [ -e "$exercise/.prob-spec" ] && rm "$exercise/.prob-spec"
+        ln -s "../../../problem-specifications/exercises/$name" "$exercise/.prob-spec"
+    fi
+done

docs/CONTRIBUTING.md

@@ -101,6 +101,11 @@ Find some tips about writing tera templates [in the next section](#tera-template
 The full documentation for tera templates is [here][tera-docs].
 Following are some approaches that have worked for our specific needs.
 
+You will likely want to look at the exercise's `canonical-data.json`
+to see what structure your input data has.
+You can use `bin/symlink_problem_specifications.sh` to have this data
+symlinked into the actual exercise directory. Handy!
+
 The name of the input property is different for each exercise.
 The default template will be something like this:
 

exercises/practice/doubly-linked-list/.docs/instructions.md

@@ -3,11 +3,7 @@
 Write a doubly linked list using unsafe Rust, including an iterator over the list
 and a cursor for efficient mutation.
 
-The doubly linked list is a fundamental data structure in computer science,
-often used in the implementation of other data structures. They're
-pervasive in functional programming languages, such as Clojure, Erlang,
-or Haskell, but far less common in imperative languages such as Ruby or
-Python.
+The doubly linked list is a fundamental data structure in computer science.
 
 Each node in a doubly linked list contains data and pointers to the next
 and previous node, if they exist.