Update the README TOC and add script that can generate it

script/markdown-toc

@@ -0,0 +1,31 @@
+#!/usr/bin/env python
+
+from re import compile
+from sys import stdin
+
+splitter = compile(r'\s+')
+
+in_pre = False
+headings = []
+for line in stdin:
+    if line.startswith('```'):
+        in_pre = not in_pre
+    if in_pre or not line.startswith('#'):
+        continue
+    level, heading = splitter.split(line, 1)
+    if 'Table of Contents' in heading:
+        continue
+    headings.append((len(level), heading.strip()))
+
+# ignore the first one, it's more of a title
+headings.pop(0)
+
+print('\n## Table of Contents\n')
+min_level = min(h[0] for h in headings)
+for heading in headings:
+    level = heading[0] - min_level
+    pre = ' ' * (level * 3)
+    title = heading[1]
+    link = title.lower().replace(' ', '-').replace('`', '')
+    print(f'{pre}* [{title}](#{link})')
+print()