docs: Add short description and simplify readme for pypi

pyproject.toml

@@ -1,10 +1,10 @@
 [tool.poetry]
 name = "guppylang"
 version = "0.1.0"
-description = ""
+description = "Pythonic quantum-classical programming language"
 authors = ["Mark Koch <[email protected]>"]
 license = "Apache-2.0"
-readme = "README.md"
+readme = "quickstart.md"
 repository = "https://github.com/CQCL/guppy"
 
 [tool.poetry.dependencies]

quickstart.md

@@ -0,0 +1,24 @@
+Guppy is a quantum programming language that is fully embedded into Python. It
+allows you to write high-level hybrid quantum programs with classical control
+flow and mid-circuit measurements using Pythonic syntax:
+
+```python
+from guppylang import guppy, Qubit, quantum
+
+guppy.load(quantum)
+
+# Teleports the state in `src` to `tgt`.
+@guppy
+def teleport(src: Qubit, tgt: Qubit) -> Qubit:
+   # Create ancilla and entangle it with src and tgt
+   tmp = Qubit()
+   tmp, tgt = cx(h(tmp), tgt)
+   src, tmp = cx(src, tmp)
+
+   # Apply classical corrections
+   if measure(h(src)):
+      tgt = z(tgt)
+   if measure(tmp):
+      tgt = x(tgt)
+   return tgt
+```