rearrange doc

Author: floatingCatty

docs/advanced/dftb.md renamed to docs/advanced/sktb/dftb.md

@@ -0,0 +1,12 @@
+=================================================
+SKTB Advanced
+=================================================
+
+.. toctree::
+   :maxdepth: 1
+   :caption: Examples
+
+   dftb
+   dptb_env
+   nrl_tb
+   soc

docs/advanced/dptb_env.md renamed to docs/advanced/sktb/dptb_env.md

@@ -31,10 +31,8 @@ These capabilities make **DeePTB** adaptable to various research scenarios, exte
 .. toctree::
    :maxdepth: 2
    :caption: Advanced
-
-   advanced/dptb_env
-   advanced/soc
-   advanced/nrl_tb
+   
+   advanced/sktb/index
    advanced/elec_properties/index
    advanced/interface/index