Add guide for CommonJS (closes #465)

packages/docs/src/content/docs/guides/commonjs.md

@@ -0,0 +1,66 @@
+---
+title: Working with CommonJS
+---
+
+CommonJS is the JavaScript module system using `require()` and `module.exports`
+statements.
+
+Knip works well with CommonJS. You don't need to use ES Modules or a
+`tsconfig.json` to use Knip. But due to the dynamic nature of CommonJS, we'll
+have to agree on a few conventions. Those conventions are designed to minimize
+impact on existing codebases, improve consistency, and ease migration to ES
+Modules or TypeScript.
+
+For **named exports**, the recommendation is to assign keys to `module.exports`:
+
+```js
+const B = function () {};
+
+module.exports.A = { option: true };
+module.exports.B = B;
+```
+
+Alternatively, assign an object with ONLY shorthand property assignments to
+`module.exports`:
+
+```js
+const A = function () {};
+const B = { option: true };
+
+module.exports = { A, B };
+```
+
+Anything else assigned to `module.exports` is considered a default export, and
+should be imported as such.
+
+The following **default import** of the **named exports** above will result in
+all those exports reported as unused, even when referenced like below:
+
+```js
+const DefaultImport = require('./common.js');
+const runtime = [DefaultImport.A, DefaultImport.B];
+```
+
+Instead, do this:
+
+```js
+const { A, B } = require('./common.js');
+const runtime = [A, B];
+```
+
+Not recommended per se, but the following import syntax also results in the
+named export `A` being used:
+
+```js
+const runtime = [require('./common.js').A];
+```
+
+Add a non-shorthand property to turn the named object notation into a single
+**default export**:
+
+```js
+const A = function () {};
+const B = { option: true };
+
+module.exports = { __esModule: true, A, B };
+```

packages/docs/src/content/docs/guides/handling-issues.md

@@ -1,5 +1,7 @@
 ---
 title: Handling Issues
+sidebar:
+  order: 2
 ---
 
 A long list of unused items can be frustrating. The list may contain false