add 'random' library docs

doc/en/scripting/builtins/librandom.md

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+# *random* library
+
+A library of functions for generating random numbers.
+
+## Non-deterministic numbers
+
+```lua
+-- Generates a random number in the range [0..1)
+random.random() --> number
+
+-- Generates a random integer in the range [0..n]
+random.random(n) --> number
+
+-- Generates a random integer in the range [a..b]
+random.random(a, b) --> number
+
+-- Generates a random byte array of length n
+random.bytes(n: number) -> Bytearray
+
+-- Generates a UUID version 4
+random.uuid() -> str
+```
+
+## Pseudorandom numbers
+
+The library provides the Random class - a generator with its own isolated state.
+
+```lua
+local rng = random.Random()
+
+-- Used similarly to math.random
+local a = rng:random() --> [0..1)
+local b = rng:random(10) --> [0..10]
+local c = rng:random(5, 20) --> [5..20]
+
+-- Sets the generator state to generate a reproducible sequence of random numbers
+rng:seed(42)
+```