add examples for stochastic KG

Author: Qianruipku

examples/stochastic/cond_Si/INPUT

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+INPUT_PARAMETERS
+#Parameters (1.General)
+suffix          Si
+calculation     scf
+esolver_type    sdft
+nbands          10
+nbands_sto      40
+nche_sto        120
+seed_sto        20000
+symmetry        1
+kpar            1
+bndpar          2
+
+#Parameters (2.Iteration)
+ecutwfc         40
+scf_thr         1e-6
+scf_nmax        100
+
+#Parameters (3.Basis)
+basis_type      pw
+
+#Parameters (4.Smearing)
+smearing_method     fd
+smearing_sigma      0.6
+
+#Parameters (5.Mixing)
+mixing_type     broyden
+mixing_beta     0.4
+
+#Parameters (6.Conductivity)
+cal_cond         1
+cond_smear       1
+cond_fwhm        0.4
+cond_wcut        20
+cond_dw          0.02
+cond_dt          0.1

examples/stochastic/cond_Si/KPT

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+K_POINTS
+0
+Gamma
+1 1 1 0 0 0