correct typos in app description at the app store

[Svetlana-T]

https://appcenter.elementary.io/com.github.bcedu.valasimplehttpserver/

"Just start Vserver in you computer" -> "Just start Vserver in your computer"

"It has been developed to follow the same behaviour than the wellknown python's simpleHTTPserver." -> "It has been developed to follow the same behaviour as the wellknown python's simpleHTTPserver."

"It also works throught comand line options." -> "It also works through command line options."