DOCUMENTATION: Document quirky behavior of ns.flags when default value is nullish (#2528)

markdown/bitburner.ns.flags.md

@@ -62,6 +62,8 @@ We support 2 forms:
 
 - Long form: the flag contains more than 1 character, e.g. --version.
 
+Note that if an argument is given and its default value is nullish, the parsed value will be a string. This may cause subtle issues if you are not careful with type coercion.
+
 ## Example
 
 
@@ -93,3 +95,21 @@ export async function main(ns) {
 // {"_":[],"delay":0,"server":"foodnstuff","exclude":[],"help":false,"v":true}
 ```
 
+```js
+export async function main(ns) {
+  const data = ns.flags([
+    ["foo", null],
+    ["bar", undefined],
+  ]);
+  console.log(data);
+}
+
+// [home /]> run example.js
+// { _: [], foo: null, bar: undefined }
+// [home /]> run example.js --foo 1000
+// { _: [], foo: "1000", bar: undefined }
+// [home /]> run example.js --foo 1000 --bar false
+// { _: [], foo: "1000", bar: "false" }
+```
+`bar` in the last example is `"false"` (a string), not `false` (a boolean). `data.bar` is truthy, not falsy.
+