add TODO in the README.md

Author: hnes

README.md

@@ -42,6 +42,7 @@ Issues and PRs are welcome 🎉🎉🎉
          * [Red Zone](#red-zone)
          * [Stack Pointer](#stack-pointer)
    * [Best Practice](#best-practice)
+   * [TODO](#todo)
    * [Donation](#donation)
 * [Copyright and License](#copyright-and-license)
 
@@ -823,6 +824,10 @@ void co_fp1() {
 }
 ```
 
+# TODO
+
+* Remove the restrictions on the GCC version (>= 5.0 currently).
+
 # Donation
 
 I'm a full-time open source developer. Any amount of the donations will be highly appreciated and could bring me great encouragement.