add codingstyle.md

Former-commit-id: 6f65784f8b0588351b1b89329bfaa59081630f50

CODING_STYLE.md

@@ -0,0 +1,19 @@
+### Please use the following code style/guidelines
+
+- use QT wherever it's possible (except there is a good reason)
+- use unix line endings (not windows)
+- indent your code with TABs instead of spaces
+- follow this rule for curly brackets
+```
+bad:
+if (conditon) {
+  code
+}
+
+good:
+if (condition)
+{
+ code
+}
+
+```