basic docs

book/src/language-tour/variables.md

@@ -1 +1,17 @@
 # Variables
+
+Function variables with types
+```
+fn add(a:Int, b:Int) -> Int {
+    a + b
+}
+```
+
+Let bindings
+```
+fn something(){
+    let a = 3
+    let b = 5
+    a + b
+}
+```