docs: add nested map example. Closes #15751 (#15753)

doc/docs.md

@@ -24,9 +24,9 @@ It is easy, and it takes only a few seconds:
 [https://github.com/vlang/v#installing-v](https://github.com/vlang/v#installing-v---from-source-preferred-method)
 
 ## Upgrading V to latest version
-If V is already installed on a machine, it can be upgrade to latest version 
+If V is already installed on a machine, it can be upgraded to its latest version
 by using the V's built-in self-updater.
-To upgrade the version run the command ` v up`
+To do so, run the command `v up`.
 
 ## Table of Contents
 
@@ -1278,6 +1278,19 @@ val2 := arr[333]?
 println(val2)
 ```
 
+V also supports nested maps:
+```v
+mut m := map[string]map[string]int{}
+m['greet'] = {
+	'Hello': 1
+}
+m['place'] = {
+	'world': 2
+}
+m['code']['orange'] = 123
+print(m)
+```
+
 Maps are ordered by insertion, like dictionaries in Python. The order is a
 guaranteed language feature. This may change in the future.