added ts string literal types

docs/typescript/string-literal-types.md

@@ -0,0 +1,22 @@
+# String Literal Types
+
+String literal types are a powerful feature in TypeScript that allows you to specify exact string values a variable can hold. This is useful for creating more precise types and can help catch errors at compile time.
+
+## Example
+
+```typescript
+const DIRECTIONS = ["left", "right", "up", "down"] as const;
+type Direction = typeof DIRECTIONS[number];
+
+// Usage
+function move(direction: Direction) {
+  // ...
+}
+
+// Array Usage
+for (const dir of DIRECTIONS) {
+  move(dir);
+}
+```
+
+In the above examples you can see how we can both use the `Direction` type directly and also leverage the `DIRECTIONS` array for type-safe values.