add readme

README.md

@@ -0,0 +1,29 @@
+<img src="example.png" width="500px"/>
+
+## rntviewer
+This is a work-in-progress interactive visualization tool for [RNTuple](https://root.cern.ch/doc/v618/md_tree_ntuple_v7_doc_README.html).
+
+### Getting the repo
+Clone this repository with 
+```
+$ git clone --recurse-submodules <repo_url>
+```
+
+### Dependencies
+rntviewer currently only works on Linux (PRs welcome).
+
+The dependencies are:
+  - GLFW3 (`libglfw3-dev` on debian, `glfw-devel` on fedora, `glfw` on arch)
+  - ROOT (likely bleeding edge version, compiled from sources)
+
+Other than those, rntviewer depends on Dear ImGui and GLAD (both included in the source tree).
+
+The machine must support OpenGL 4.
+
+### Building
+Building is done with `make`. Make sure to `source /path/to/root/bin/thisroot.sh` before running it.
+
+### Usage
+```
+$ ./rntviewer <ntuple_name> <ntuple_file.root>
+```

imgui.ini

@@ -8,9 +8,13 @@ Size=1152,1414
 
 [Window][main]
 Pos=0,0
-Size=1143,1388
+Size=1211,806
 
 [Window][Hex View]
 Pos=91,62
 Size=1002,939
 
+[Table][0x9FEC56E3,2]
+Column 0  Weight=1.6105
+Column 1  Weight=0.3895
+