rune/libenclave: Supply the missing return value description information for PAL API v2
@@ -18,7 +18,7 @@ N/A
### Return value
```
-N/A
+@int: the PAL API version of the current enclave runtime.
```
## 2.pal_init()
@@ -107,6 +107,13 @@ int pal_exec(struct pal_exec_args *attr);
@exit_value: The exit value of the process.
```
+### Return value
+```
+0: Success
+-EINVAL: Invalid argument
+-ENOSYS: The function is not supported
+```
+
## 5.pal_kill()
### Description
