docs: Add some doc string to the scripts

scripts/lock2nix.py

@@ -1,3 +1,9 @@
+'''
+This script generates a .nix file containing all dependencies specified in the
+special lock file. The .nix file also contains the derivation "pubCache", which can
+be used as the path in the PUB_CACHE environment variable.
+'''
+
 import sys
 import yaml
 import urllib.parse

scripts/pubspec2lock.py

@@ -1,3 +1,9 @@
+'''
+Takes a Dart pubspec.lock file as input and outputs a specialized lock file
+that contains archive URLs and sha256 hashes for nix. Only useful in combination
+with lock2nix.py.
+'''
+
 import sys
 import subprocess
 import urllib