Update README.md -- update the overview table for tuners part (#1843)

* Update README.md -- update the tuners part of the overview table.

README.md

@@ -80,47 +80,58 @@
         </ul>
       </td>
       <td align="left" >
-        <a href="docs/en_US/Tuner/BuiltinTuner.md">Tuner</a>
+        <a href="docs/en_US/Tuner/BuiltinTuner.md">Hyperparameter Tuning</a>
+        <ul>
+          <b>Exhaustive search</b>
           <ul>
             <li><a href="docs/en_US/Tuner/BuiltinTuner.md#Random">Random Search</a></li>
+            <li><a href="docs/en_US/Tuner/BuiltinTuner.md#GridSearch">Grid Search</a></li>
+            <li><a href="docs/en_US/Tuner/BuiltinTuner.md#Batch">Batch</a></li>
+            </ul>
+          <b>Heuristic search</b>
+          <ul>
             <li><a href="docs/en_US/Tuner/BuiltinTuner.md#Evolution">Naïve Evolution</a></li>
-          <li><a href="docs/en_US/Tuner/BuiltinTuner.md#TPE">TPE</a></li>
             <li><a href="docs/en_US/Tuner/BuiltinTuner.md#Anneal">Anneal</a></li>  
-          <li><a href="docs/en_US/Tuner/BuiltinTuner.md#SMAC">SMAC</a></li>
-          <li><a href="docs/en_US/Tuner/BuiltinTuner.md#Batch">Batch</a></li>
-          <li><a href="docs/en_US/Tuner/BuiltinTuner.md#GridSearch">Grid Search</a></li>
             <li><a href="docs/en_US/Tuner/BuiltinTuner.md#Hyperband">Hyperband</a></li>
-          <li><a href="docs/en_US/Tuner/BuiltinTuner.md#MetisTuner">Metis Tuner</a></li>
+          </ul>
+          <b>Bayesian optimization</b>
+            <ul>
               <li><a href="docs/en_US/Tuner/BuiltinTuner.md#BOHB">BOHB</a></li>  
-          <li><a href="docs/en_US/Tuner/BuiltinTuner.md#GPTuner">GP Tuner</a></li>
-          <li><a href="docs/en_US/Tuner/BuiltinTuner.md#PPOTuner">PPO Tuner</a></li>
-          <li><a href="docs/en_US/Tuner/BuiltinTuner.md#NetworkMorphism">Network Morphism</a></li>
+              <li><a href="docs/en_US/Tuner/BuiltinTuner.md#TPE">TPE</a></li>
+            <li><a href="docs/en_US/Tuner/BuiltinTuner.md#SMAC">SMAC</a></li> 
+            <li><a href="docs/en_US/Tuner/BuiltinTuner.md#MetisTuner">Metis Tuner</a></li>
+            <li><a href="docs/en_US/Tuner/BuiltinTuner.md#GPTuner">GP Tuner</a> </li>
             </ul>  
-          <a href="docs/en_US/Assessor/BuiltinAssessor.md">Assessor</a>
+          <b>RL Based</b>
           <ul>
-          <li><a href="docs/en_US/Assessor/BuiltinAssessor.md#Medianstop">Median Stop</a></li>
-          <li><a href="docs/en_US/Assessor/BuiltinAssessor.md#Curvefitting">Curve Fitting</a></li>   
+            <li><a href="docs/en_US/Tuner/BuiltinTuner.md#PPOTuner">PPO Tuner</a> </li>
           </ul>
-          <a href="docs/en_US/NAS/Overview.md">NAS (Beta)</a>
+        </ul>
+          <a href="docs/en_US/NAS/Overview.md">Neural Architecture Search</a>
           <ul>
           <li><a href="docs/en_US/NAS/Overview.md#enas">ENAS</a></li>
           <li><a href="docs/en_US/NAS/Overview.md#darts">DARTS</a></li>
           <li><a href="docs/en_US/NAS/Overview.md#p-darts">P-DARTS</a></li>
+          <li><a href="docs/en_US/Tuner/BuiltinTuner.md#NetworkMorphism">Network Morphism</a> </li>
           </ul>
-          <a href="docs/en_US/Compressor/Overview.md">Model Compression (Beta)</a>
+          <a href="docs/en_US/Compressor/Overview.md">Model Compression</a>
           <ul>
           <li><a href="docs/en_US/Compressor/Pruner.md#agp-pruner">AGP Pruner</a></li>
           <li><a href="docs/en_US/Compressor/Pruner.md#slim-pruner">Slim Pruner</a></li>
           <li><a href="docs/en_US/Compressor/Pruner.md#fpgm-pruner">FPGM Pruner</a></li>
           <li><a href="docs/en_US/Compressor/Quantizer.md#qat-quantizer">QAT Quantizer</a></li>
           <li><a href="docs/en_US/Compressor/Quantizer.md#dorefa-quantizer">DoReFa Quantizer</a></li>
-          <li><a href="docs/en_US/Compressor/Overview.md">More...</a></li>
           </ul>
           <a href="docs/en_US/FeatureEngineering/Overview.md">Feature Engineering (Beta)</a>
           <ul>
           <li><a href="docs/en_US/FeatureEngineering/GradientFeatureSelector.md">GradientFeatureSelector</a></li>
           <li><a href="docs/en_US/FeatureEngineering/GBDTSelector.md">GBDTSelector</a></li>
           </ul>
+          <a href="docs/en_US/Assessor/BuiltinAssessor.md">Early Stop Algorithms</a>
+          <ul>
+          <li><a href="docs/en_US/Assessor/BuiltinAssessor.md#Medianstop">Median Stop</a></li>
+          <li><a href="docs/en_US/Assessor/BuiltinAssessor.md#Curvefitting">Curve Fitting</a></li>   
+          </ul>
       </td>
       <td>
       <ul>