add `.editorconfig`

ease the view and edit settings of the editor/IDE

more info see https://editorconfig.org/

.editorconfig

@@ -0,0 +1,24 @@
+# https://editorconfig.org/
+
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+
+tab_width = 8
+indent_size = 2
+ij_continuation_indent_size = 4
+indent_style = space
+
+trim_trailing_whitespace = true
+
+
+[*.{java,j}]
+indent_size = 4
+ij_continuation_indent_size = 8
+
+
+[*.md]
+trim_trailing_whitespace = false