Make OTP installation optional (#81)

test-projects/gleam_gleam/test/gleam_gleam_test.gleam

@@ -0,0 +1,12 @@
+import gleeunit
+import gleeunit/should
+
+pub fn main() {
+  gleeunit.main()
+}
+
+// gleeunit test functions end in `_test`
+pub fn hello_world_test() {
+  1
+  |> should.equal(1)
+}