misc: create backwards-compatibility README for system design (#164)

* Create readme for redirecting viewers from medium

The link from task11 in https://medium.com/free-code-camp/the-ultimate-guide-to-preparing-for-the-coding-interview-183251ee36c9 is broken. Fixing it by providing a reference to the right url

* Update README.md

* Update README.md

Co-authored-by: Yangshun Tay <tay.yang.shun@gmail.com>

design/README.md

@@ -0,0 +1,5 @@
+# System Design
+
+## Specific topics
+
+The contents have been moved to a different [location](../experimental/design#specific-topics).