Update issue_template.md

.github/issue_template.md

@@ -1,2 +1,7 @@
-(Please read guidelines in https://github.com/ocornut/imgui/blob/master/.github/CONTRIBUTING.md then delete this line)
+(Please carefully read guidelines in [CONTRIBUTING.md](https://github.com/ocornut/imgui/blob/master/.github/CONTRIBUTING.md) then delete this line)
 
+You can include code this way:
+```cpp
+ImGui::Begin("Hello");
+ImGui::ThisIsMoreCode();
+```