Add package name to header

Author: matt-graham

README.md

@@ -2,7 +2,7 @@
 
 <img class="dark-light" width="98" height="85" alt="s2fft logo - schematic representation of a tiled sphere" src="https://raw.githubusercontent.com/astro-informatics/s2fft/main/docs/assets/sax_logo.png">
 
-# Differentiable and accelerated spherical transforms
+# S2FFT: differentiable and accelerated spherical transforms
 
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