Add code snippet for random projection

Author: relf

docs/website/content/snippets/random-projection.md

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+title = "Gaussian Random Projection"
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+```rust
+// Assume we get some training data like MNIST: 60000 samples of 28*28 images (ie dim 784)
+let dataset = Dataset::from(Array::<f64, _>::random((60000, 28 * 28), Standard));
+
+// We can work in a reduced dimension using a Gaussian Random Projection
+let reduced_dim = 100;
+let proj = GaussianRandomProjection::<f32>::params()
+    .target_dim(reduced_dim)
+    .fit(&dataset)?;
+let reduced_ds = proj.transform(&dataset);
+
+println!("New dataset shape: {:?}", reduced_ds.records().shape());
+// -> New dataset shape: [60000, 100]
+```