[DOC] add the intro, modify the document structure

docs/index.rst

@@ -7,7 +7,7 @@
 ``Learnware`` Documentation
 ============================================================
 
-``Learnware`` is ...
+``Learnware`` is a model sharing platform, which give a basic implementation of the learnware paradigm. A learnware is a well-performed trained machine learning model with a specification that enables it to be adequately identified to reuse according to the requirement of future users who may know nothing about the learnware in advance. The learnware paradigm can solve entangled problems in the current machine learning paradigm, like continual learning and catastrophic forgetting. It also reduces resources for training a well-performed model. 
 
 .. _user_guide:
 
@@ -26,6 +26,10 @@ Document Structure
    Introduction <start/intro.rst>
    Quick Start <start/quick.rst>
    Installation Guide <start/install.rst>
+   Workflow
+      Submit learnware <workflow/submit.rst>
+      Identify helpful learnware <workflow/Identify helpful learnwares.rst>
+      Reuse learnware <workflow/reuse.rst>
 
 .. toctree::
    :maxdepth: 3