feat(docs): document E0358

docs/errors/E0358.md

@@ -0,0 +1,23 @@
+# E0358: 'declare' should not be written inside a 'declare namespace'
+
+Inside `declare namespace`, declarations (functions, classes, etc.) are
+automatically `declare`. It is a syntax error to explicitly write `declare` on
+these declarations:
+
+```typescript
+declare namespace jQuery {
+  declare function get(url);
+}
+```
+
+To fix this error, remove the `declare` keyword:
+
+```typescript
+declare namespace jQuery {
+  function get(url);
+}
+```
+
+Known issues with quick-lint-js:
+* [possible false positive with 'declare' inside 'declare
+  module'](https://github.com/quick-lint/quick-lint-js/issues/1142)