Add comment clarifying isNotNeededPackage (#17321)

Author: Andy

src/compiler/moduleNameResolver.ts

@@ -256,6 +256,8 @@ namespace ts {
                         for (const typeDirectivePath of host.getDirectories(root)) {
                             const normalized = normalizePath(typeDirectivePath);
                             const packageJsonPath = pathToPackageJson(combinePaths(root, normalized));
+                            // `types-publisher` sometimes creates packages with `"typings": null` for packages that don't provide their own types.
+                            // See `createNotNeededPackageJSON` in the types-publisher` repo.
                             // tslint:disable-next-line:no-null-keyword
                             const isNotNeededPackage = host.fileExists(packageJsonPath) && readJson(packageJsonPath, host).typings === null;
                             if (!isNotNeededPackage) {