Add Map.from_struct and Kernel.struct to maps section of Elixir cheatsheet (#1631)

* Update elixir.md

Added Map.from_struct and Kernel.struct to maps section.

* Update elixir.md

Co-authored-by: Rico Sta. Cruz <rstacruz@users.noreply.github.com>

elixir.md

@@ -429,6 +429,20 @@ Map.new([a: 1, b: 2])
 Map.new([:a, :b], fn x -> {x, x} end)  # → %{a: :a, b: :b}
 ```
 
+### Working with structs
+
+#### Struct to map
+
+```elixir
+Map.from_struct(%AnyStruct{a: "b"})  # → %{a: "b"}
+```
+
+#### Map to struct
+
+```elixir
+struct(AnyStruct, %{a: "b"})  # → %AnyStruct{a: "b"}
+```
+
 ## List
 
 ```elixir