Change git clone command in getting started

Changed git clone to git clone to git clone --depth=1 to reduce the cloning size as this is only for deployment of mycroft and not for development and  added additional instructions for developers to use the whole repo instead of single depth repo.

README.md

@@ -27,15 +27,21 @@ Mycroft is a hackable open source voice assistant.
 
 First, get the code on your system!  The simplest method is via git ([git installation instructions](https://gist.github.com/derhuerst/1b15ff4652a867391f03)):
 - `cd ~/`
-- `git clone https://github.com/MycroftAI/mycroft-core.git`
+- `git clone --depth=1 https://github.com/MycroftAI/mycroft-core.git`
 - `cd mycroft-core`
 - `bash dev_setup.sh`
 
+
 This script sets up dependencies and a [virtualenv][about-virtualenv].  If running in an environment besides Ubuntu/Debian, Arch or Fedora you may need to manually install packages as instructed by dev_setup.sh.
 
 [about-virtualenv]:https://virtualenv.pypa.io/en/stable/
 
 NOTE: The default branch for this repository is 'dev', which should be considered a work-in-progress. If you want to clone a more stable version, switch over to the 'master' branch.
+NOTE: If you are willing to contribute to this project, clone the entire repository by 
+- `git clone  https://github.com/MycroftAI/mycroft-core.git`
+ instead of 
+- `git clone --depth=1 https://github.com/MycroftAI/mycroft-core.git`
+which is said above.
 
 # Running Mycroft