add basic docs for lang things (#484)

Signed-off-by: Jess Frazelle <github@jessfraz.com>

docs/kcl/types.md

@@ -0,0 +1,75 @@
+# Types
+
+`KCL` defines the following types and keywords the language.
+
+All these types can be nested in various forms where nesting applies. Like
+arrays can hold objects and vice versa.
+
+## Boolean
+
+`true` or `false` work when defining values.
+
+## Variable declaration
+
+Variables are defined with the `let` keyword like so:
+
+```
+let myBool = false
+```
+
+## Array
+
+An array is defined with `[]` braces. What is inside the brackets can
+be of any type. For example, the following is completely valid:
+
+```
+let myArray = ["thing", 2, false]
+```
+
+If you want to get a value from an array you can use the index like so:
+`myArray[0]`.
+
+
+## Object
+
+An object is defined with `{}` braces. Here is an example object:
+
+```
+let myObj = {a: 0, b: "thing"}
+```
+
+We support two different ways of getting properties from objects, you can call
+`myObj.a` or `myObj["a"]` both work.
+
+
+## Functions
+
+We also have support for defining your own functions. Functions can take in any
+type of argument. Below is an example of the syntax:
+
+```
+fn myFn = (x) => {
+  return x
+}
+```
+
+As you can see above `myFn` just returns whatever it is given.
+
+
+## Binary expressions
+
+You can also do math! Let's show an example below:
+
+```
+let myMathExpression = 3 + 1 * 2 / 3 - 7
+```
+
+You can nest expressions in parenthesis as well:
+
+```
+let myMathExpression = 3 + (1 * 2 / (3 - 7))
+```
+
+Please if you find any issues using any of the above expressions or syntax
+please file an issue with the `ast` label on the [modeling-app
+repo](https://github.com/KittyCAD/modeling-app/issues/new).