feat: add imported NanoAOD RNTuple (#186)

Author: ariostas

dev/make-root/rntuple_imported_NanoAOD.md

@@ -0,0 +1,8 @@
+First, obtain a TTree-based NanoAOD file. Then, run the following commands in ROOT.
+
+```cpp
+auto importer = ROOT::Experimental::RNTupleImporter::Create("./cmsopendata2015_ttbar_19980_NANOAOD.root", "Events", "./cmsopendata2015_ttbar_19980_NANOAOD_RNTupleImporter_rntuple_v1-0-0-1.root");
+auto c = importer.get();
+c->SetMaxEntries(10);
+c->Import()
+```