add README.md

README.md

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-Translate 2D/3D images by phase shifting Fourier transforms in PyTorch.
+*torch-fourier-shift* is a package for shifting 2D and 3D images with subpixel precision 
+by applying phase shifts to Fourier transforms in PyTorch.
+
+<figure markdown>
+  ![A very simple example](./assets/shift_2d_image.png){ width="500" }
+  <figcaption>Shifting a 2D image with torch-fourier-shift</figcaption>
+</figure>
+
+
+```python
+import torch
+from torch_fourier_shift import fourier_shift_image_2d
+
+# create a dummy image
+my_image = torch.tensor(
+    [[0, 0, 0, 0, 0, 0],
+     [0, 1, 0, 0, 0, 0],
+     [0, 0, 0, 0, 0, 0],
+     [0, 0, 0, 0, 0, 0],
+     [0, 0, 0, 0, 0, 0],
+     [0, 0, 0, 0, 0, 0]]
+)
+
+# shift the image by 1 pixel in dim 0, 2 pixels in dim 1
+shifted_image = fourier_shift_image_2d(image=my_image, shifts=torch.tensor([1, 2]))
+```
+
+## Installation
+
+*torch-fourier-shift* is available on PyPI.
+
+```shell
+pip install torch-fourier-shift
+```
+
+## Usage
+
+Please check the the docs at [teamtomo.org/torch-fourier-shift](https://teamtomo.org/torch-fourier-shift/)