Fixed several typos
Added node_modules to .gitignore

This is helpful if you work with a local installation of gitbook.
Replaced computer disk with harddisk
Fixed example, the text above says one should type python3 in the terminal
Fixed typo, the server is being asked, so it should be "it" instead of "you"
Merge pull request #32 from keimlink/fixes-and-improvements

Fixes and improvements