added the link to doc

README.md

-# CSST
+## CSST
 
 CSST pipeline.
+
+
+## install
+```
+pip install -U git+git://github.com/hypergravity/laspec
+```
+
+
+## doc
+
+[ https://laspec.readthedocs.io/en/latest/]( https://laspec.readthedocs.io/en/latest/)
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