nix: setup direnv

Author: arntanguy

.envrc

@@ -0,0 +1,5 @@
+if command -v nix >/dev/null; then
+  use flake
+fi
+
+export PYTHONPATH="$PWD/build/python/Release:$PYTHONPATH"

.gitignore

@@ -5,3 +5,5 @@ eigen/eigen.pxd
 *.cpp
 setup.py
 build
+result*
+.direnv/

README.md

@@ -20,6 +20,38 @@ If you want more features feel free to open an issue or submit a pull request. :
 Installing
 ------
 
+### Nix
+
+#### Run
+
+To get a python shell with Eigen3ToPython installed
+
+```sh
+nix run github:jrl-umi3218/Eigen3ToPython
+```
+
+Then
+```python
+import eigen
+```
+
+#### Develop
+
+To develop, use
+
+```
+gh repo clone jrl-umi3218/Eigen3ToPython
+direnv allow # activates a nix develop environment and set the python path
+cmake -B build $cmakeFlags
+cmake --build build
+```
+
+Then
+```python
+import eigen
+# latest bindings built from source
+```
+
 ### Ubuntu LTS (22.04, 24.04, 26.04)
 
 You must first setup our package mirror: