fix(guide): simplify directory structure

guide/english/csharp/literal-improvements/index.md

@@ -0,0 +1,20 @@
+---
+title: Literal Improvements
+---
+
+# Literal Improvements
+
+C# 7.0 allows _ to occur as a ***digit separator*** inside number literals:
+
+```
+var d = 123_456;
+var x = 0xAB_CD_EF;
+```
+
+You can put them wherever you want between digits, to improve readability. They have no effect on the value.
+
+Also, C# 7.0 introduces ***binary literals***, so that you can specify bit patterns directly instead of having to know hexadecimal notation by heart.
+
+```
+var b = 0b1010_1011_1100_1101_1110_1111;
+```