fix links (#20748)

The original link page was not found, the main branch of sui does not
contain the path crates/sui-framework/src/natives/mod.rs. This PR
changes it to
https://github.com/MystenLabs/sui/blob/main/external-crates/move/crates/move-stdlib-natives/src/lib.rs#L146

crates/sui-framework/README.md

@@ -3,7 +3,7 @@
 1. Add a new `./sui-framework/{name}.move` file or find an appropriate `.move`.
 2. Add the signature of the function you are adding in `{name}.move`. 
 3. Add the rust implementation of the function under `./sui-framework/src/natives` with name `{name}.rs`.
-4. Link the move interface with the native function in [all_natives](https://github.com/MystenLabs/sui/blob/main/crates/sui-framework/src/natives/mod.rs#L23)
+4. Link the move interface with the native function in [all_natives](https://github.com/MystenLabs/sui/blob/main/external-crates/move/crates/move-stdlib-natives/src/lib.rs#L146)
 5. Write some tests in `{name}_tests.move` and pass `run_framework_move_unit_tests`.
 6. Optionally, update the mock move VM value in [gas_tests.rs](https://github.com/MystenLabs/sui/blob/276356e168047cdfce71814cb14403f4653a3656/crates/sui-core/src/unit_tests/gas_tests.rs) since the sui-framework package will increase the gas metering.
 7. Optionally, run `cargo insta test` and `cargo insta review` since the sui-framework build will change the empty genesis config.