add stringswitch

[fabdurso]

• Project Name: StringSwitch
• Project URL: https://stringswitch.com
• Project Description: Easily convert iOS .strings files to Android strings.xml format and vice versa.
• Why it should be added to awesome-swift:
• At least 15 stars (GitHub project)
• Support Swift 5
• Updated contents.json instead of README
• Lib is fully open sourced, written in Swift and not a wrapper over compiled lib
• Description does not say "written in Swift" or variant 🤓

[vpeschenkov]

@fabdurso thanks!