fix(docs): restore jsligo keywords

[timothymcmackin]

We removed the list of JsLIGO keywords because you can no longer escape them, but it seems to me that we should still have a list of reserved words, because using these words as variable names can crash the compiler. For example, I'll post a contract below that seems to lock up the compiler.

@EduardoRFS This is the list of keywords from jsligo 1.x with the @ keywords removed because apparently you can't create a variable name that starts with @. Is there a way to get the full list from the code?

type storage_type = nat;
type return_type = [list<operation>, storage_type];

class Counter {

  @entry
  static add = (value: nat, store: storage_type): return_type => {
    const else = 5 as nat;
    const export = 5 as nat;
    const false = 5 as nat;
    const for = 5 as nat;
    const from = 5 as nat;
    const if = 5 as nat;
    const implements = 5 as nat;
    const interface = 5 as nat;
    const let = 5 as nat;
    const match = 5 as nat;
    const namespace = 5 as nat;
    const of = 5 as nat;
    const parameter_of = 5 as nat;
    const return = 5 as nat;
    const switch = 5 as nat;
    const true = 5 as nat;
    const type = 5 as nat;
    const when = 5 as nat;
    const while = 5 as nat;
    const sum = else + export + false + for + from + if + implements + interface + let + match + namespace + of + parameter_of + return + switch + true + type + when + while;
    return [[], store + value];
  }

  @entry
  static sub = (value: nat, store: storage_type): return_type =>
    [[], abs(store - value)];

  @view
  static getValue = (_: unit, storage: storage_type): storage_type =>
    storage;
}