docs: add bank-account design.md

Author: masiljangajji

exercises/practice/bank-account/.meta/design.md

@@ -0,0 +1,15 @@
+# Design
+
+## Analyzer
+
+This exercise could benefit from the following rules in the [analyzer](https://github.com/exercism/java-analyzer):
+
+- `essential`: Verify that the solution **guards `deposit`, `withdraw`, and `getBalance` with `synchronized`** to avoid
+  race conditions.
+- `essential`: Verify that the solution **checks the account’s open/closed state before every balance operation**
+- `essential`: If the solution **allows negative amounts** in `deposit` or `withdraw`, instruct the student to reject
+  them early.
+- `essential`: If the solution **does not throw an exception when `amount` exceeds `balance` during withdrawal**,
+  instruct the student to add this check.
+- `actionable:`: If the solution **declares zero or more than one `boolean`/`Boolean` field to track account state**,
+  instruct the student to use exactly one such field.