fix: add and fix solution links

zh-CN/src/functional-programing/closure.md

@@ -48,4 +48,5 @@ fn call_with_different_values() {
 
     assert_eq!(v2, 1);
 }
-```
+```
+> 你可以在[这里](https://github.com/sunface/rust-by-practice/blob/master/solutions/functional-programing/closure.md)找到答案(在 solutions 路径下)

zh-CN/src/functional-programing/iterator.md

@@ -1,2 +1,4 @@
 # Iterator
 
+
+> 你可以在[这里](https://github.com/sunface/rust-by-practice/blob/master/solutions/functional-programing/iterator.md)找到答案(在 solutions 路径下)

zh-CN/src/lifetime/advance.md

@@ -283,3 +283,5 @@ fn use_list(list: &List) {
     println!("{}", list.manager.text);
 }
 ```
+
+> 你可以在[这里](https://github.com/sunface/rust-by-practice/blob/master/solutions/lifetime/advance.md)找到答案(在 solutions 路径下)

zh-CN/src/lifetime/basic.md

@@ -335,3 +335,5 @@ enum Either<'a> {
 
 fn main() {}
 ```
+
+> 你可以在[这里](https://github.com/sunface/rust-by-practice/blob/master/solutions/lifetime/basic.md)找到答案(在 solutions 路径下)

zh-CN/src/lifetime/static.md

@@ -185,3 +185,5 @@ fn print_g(t: &'static String) {
   println!("{}", t);
 }
 ```
+
+> 你可以在[这里](https://github.com/sunface/rust-by-practice/blob/master/solutions/lifetime/static.md)找到答案(在 solutions 路径下)

zh-CN/src/result-panic/panic.md

@@ -109,3 +109,5 @@ note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose bac
 panic = 'abort'
 ```
 
+
+> 你可以在[这里](https://github.com/sunface/rust-by-practice/blob/master/solutions/result-panic/panic.md)找到答案(在 solutions 路径下)

zh-CN/src/result-panic/result.md

@@ -207,4 +207,5 @@ fn main() -> Result<(), ParseIntError> {
     println!("{}", number);
     Ok(())
 }
-```
+```
+> 你可以在[这里](https://github.com/sunface/rust-by-practice/blob/master/solutions/result-panic/result.md)找到答案(在 solutions 路径下)