Create CONTRIBUTING.md (#257)

CONTRIBUTING.md

@@ -0,0 +1,12 @@
+# Contributing 
+
+As app is in early stage of development, expect large codebase changes. 
+
+Complete your PR before submitting it. 
+
+If you implement something big, better create multiple PR for each small part.
+
+Don't add any *.lock files, except pubspec.lock.
+
+## Translations
+If you want to collaborate by adding your language to the application, you can do it through [our Crowdin project](https://crowdin.com/project/chameleonultragui). Do not contribute files into `chameleonultragui/lib/l10n/app_*.arb`. All translations should be added only to Crowdin. If your language is missing, you can create issue and ask to enable it. "Chameleon Ultra GUI", "Chameleon" and other trademarks should not be translated.