add readme & default disable test

README.md

@@ -0,0 +1,25 @@
+# mrubypp
+
+mruby c++ header only library
+
+## Installation
+- install mruby
+- add to cmake project, link `mrubypp` or copy *.h to you projects
+- `cmake -DMRUBYPP_BUILD_TEST=ON .` build tests
+
+## Usage
+```
+  #include "mrubypp.h"
+
+  mrubypp engine;
+  engine.load(R"(
+      def sort_and_get_first(a)
+        a.sort!
+        a[0]
+      end
+  )");
+
+  std::vector<int> a{3, 1, 2};
+  auto b = engine.call<int>("sort_and_get_first", a);
+  assert(b == 1);
+```