tutorial REAMDE

Tutorial.rst

+Getting Started on the ISC design
+=================================
+To redo the A1 ISC design, it wll be necessary to understand:
+1. the physcs of laser nterferometry
+1. moulaton / emodulaton fos signal extraction
+1. feedback loops (MIMO & SISO)
+1. how to use Fnesse/pyKat to smulate these thngs
+
+How does Finesse work?
+=======================
+https://dcc.ligo.org/LIGO-G1901578
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