Update Installation and Getstarted (#610)

* update readme in ga_squad

* update readme

* fix typo

* Update README.md

* Update README.md

* Update README.md

* update readme

* update

* fix path

* update reference

* fix bug in config file

* update nni_arch_overview.png

* update

* update

* update

* add release note

* update the README.md

* update Installation.md and Getstart.md

docs/GetStarted.md

@@ -18,7 +18,7 @@
 
 * __Install NNI through source code__
    
-      git clone -b v0.4.1 https://github.com/Microsoft/nni.git
+      git clone -b v0.5 https://github.com/Microsoft/nni.git
       cd nni
       source install.sh
 

docs/Installation.md

@@ -18,7 +18,7 @@ Currently we only support installation on Linux & Mac.
 
 * __Install NNI through source code__
    
-      git clone -b v0.4.1 https://github.com/Microsoft/nni.git
+      git clone -b v0.5 https://github.com/Microsoft/nni.git
       cd nni
       source install.sh