docs: add a section for Lambda function expressions f(|x,y|x+y) (fix #23223) (#24789)

Author: lcheylus

doc/docs.md

@@ -120,6 +120,7 @@ by using any of the following commands in a terminal:
     * [Mutable arguments](#mutable-arguments)
     * [Variable number of arguments](#variable-number-of-arguments)
     * [Anonymous & higher-order functions](#anonymous--higher-order-functions)
+    * [Lambda expressions](#lambda-expressions)
     * [Closures](#closures)
     * [Parameter evaluation order](#parameter-evaluation-order)
 * [References](#references)
@@ -3021,6 +3022,28 @@ fn main() {
 }
 ```
 
+### Lambda expressions
+
+Lambda expressions in V are small anonymous functions, defined using
+the `|variables| expression` syntax. Note: this syntax is valid only inside calls to higher
+order functions.
+
+Here are some examples:
+```v
+mut a := [1, 2, 3]
+a.sort(|x, y| x > y) // sorts the array, defining the comparator with a lambda expression
+println(a.map(|x| x * 10)) // prints [30, 20, 10]
+```
+
+```v
+// Lambda function can be used as callback
+fn f(cb fn (a int) int) int {
+	return cb(10)
+}
+
+println(f(|x| x + 4)) // prints 14
+```
+
 ### Closures
 
 V supports closures too.
@@ -8331,4 +8354,4 @@ This is the place to be, to discuss the V language, learn about latest
 developments, quickly get help with issues, witness/participate in
 ~~epic flame wars~~ constructive criticism exchanges and design decisions.
 Join it, and learn more about languages, games, editors, people, Klingons,
-Conway's law and the universe.
+Conway's law and the universe.