Changing custom shader. Add alpha cutout

  Shader "Toony Colors Free/Rim Lighting"
  {
      Properties
      {
          //TOONY COLORS
          _Color ("Color", Color) = (0.5,0.5,0.5,1.0)
          _HColor ("Highlight Color", Color) = (0.6,0.6,0.6,1.0)
          _SColor ("Shadow Color", Color) = (0.3,0.3,0.3,1.0)
          
          //DIFFUSE
          _MainTex ("Main Texture (RGB)", 2D) = "white" {}
          
          //TOONY COLORS RAMP
          _Ramp ("Toon Ramp (RGB)", 2D) = "gray" {}
          
          //RIM LIGHT
          _RimColor ("Rim Color", Color) = (0.8,0.8,0.8,0.6)
          _RimMin ("Rim Min", Range(0,1)) = 0.5
          _RimMax ("Rim Max", Range(0,1)) = 1.0
          
          _Cutoff ("Alpha Cutoff", Range(0,1)) = 0.7
      }
      
      SubShader
      {
          Tags { "RenderType"="Opaque" }
          
          CGPROGRAM
          
          #pragma surface surf ToonyColorsCustom alphatest:_Cutoff addshadow
          #pragma target 2.0
          #pragma glsl
          
          
          //================================================================
          // VARIABLES
          
          fixed4 _Color;
          sampler2D _MainTex;
          
          fixed4 _RimColor;
          fixed _RimMin;
          fixed _RimMax;
          float4 _RimDir;
          
          struct Input
          {
              half2 uv_MainTex;
              float3 viewDir;
          };
          
          //================================================================
          // CUSTOM LIGHTING
          
          //Lighting-related variables
          fixed4 _HColor;
          fixed4 _SColor;
          sampler2D _Ramp;
          
          //Custom SurfaceOutput
          struct SurfaceOutputCustom
          {
              fixed3 Albedo;
              fixed3 Normal;
              fixed3 Emission;
              half Specular;
              fixed Alpha;
          };
          
          inline half4 LightingToonyColorsCustom (SurfaceOutputCustom s, half3 lightDir, half3 viewDir, half atten)
          {
              s.Normal = normalize(s.Normal);
              fixed ndl = max(0, dot(s.Normal, lightDir)*0.5 + 0.5);
              
              fixed3 ramp = tex2D(_Ramp, fixed2(ndl,ndl));
          #if !(POINT) && !(SPOT)
              ramp *= atten;
          #endif
              _SColor = lerp(_HColor, _SColor, _SColor.a);    //Shadows intensity through alpha
              ramp = lerp(_SColor.rgb,_HColor.rgb,ramp);
              fixed4 c;
              c.rgb = s.Albedo * _LightColor0.rgb * ramp;
              c.a = s.Alpha;
          #if (POINT || SPOT)
              c.rgb *= atten;
          #endif
              return c;
          }
          
          
          //================================================================
          // SURFACE FUNCTION
          
          void surf (Input IN, inout SurfaceOutputCustom o)
          {
              fixed4 mainTex = tex2D(_MainTex, IN.uv_MainTex);
              
              o.Albedo = mainTex.rgb * _Color.rgb;
              o.Alpha = mainTex.a * _Color.a;
              
              //Rim
              float3 viewDir = normalize(IN.viewDir);
              half rim = 1.0f - saturate( dot(viewDir, o.Normal) );
              rim = smoothstep(_RimMin, _RimMax, rim);
              o.Emission += (_RimColor.rgb * rim) * _RimColor.a;
          }
          
          ENDCG
      }
      
      Fallback "Diffuse"
  }

You really should look these things up before asking the question, though. There are many different pages that cover this kind of thing, and I'm sure this question has been asked before.