Add missing links for insecure_time

Author: tesuji

src/libstd/time.rs

@@ -153,6 +153,8 @@ pub struct Instant(time::Instant);
 /// | Windows   | [GetSystemTimeAsFileTime]                                            |
 ///
 /// [clock_time_get (Realtime Clock)]: https://github.com./NuxiNL/cloudabi/blob/master/cloudabi.txt
+/// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
+/// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
 /// [gettimeofday]: http://man7.org/linux/man-pages/man2/gettimeofday.2.html
 /// [clock_gettime (Realtime Clock)]: https://linux.die.net/man/3/clock_gettime
 /// [__wasi_clock_time_get (Realtime Clock)]: https://github.com./CraneStation/wasmtime/blob/master/docs/WASI-api.md#clock_time_get