Updating documentation for cmake dtype selective build (pytorch#12112)

Updating documentation for cmake dtype selective build with model API.
Table at
`selective_build_model_doc/docs/source/kernel-library-selective-build.md`
now looks like:

![image](https://github.com/user-attachments/assets/68b7c8fe-dfc5-4ae4-9756-5599680357bf)

Fixes pytorch#12065

cc @mergennachin @byjlw

Author: BujSet

docs/source/kernel-library-selective-build.md

@@ -125,4 +125,4 @@ register_custom_kernels(); // Registers only the "custom" kernels
 This avoids relying on static initialization and enables you to register only the kernels you want.
 
 ### Compatibility
-If `--lib-name` is not passed, the default behavior remains unchanged, the codegen script will generate a general `RegisterKernels.cpp` and `register_all_kernels()` function.
+If `--lib-name` is not passed, the default behavior remains unchanged, the codegen script will generate a general `RegisterKernels.cpp` and `register_all_kernels()` function.

examples/selective_build/README.md

@@ -12,12 +12,12 @@ cd executorch
 bash examples/selective_build/test_selective_build.sh cmake
 ```
 
-Check out `CMakeLists.txt` for demo of 3 selective build APIs:
+Check out `CMakeLists.txt` for demo of selective build APIs:
 1. `SELECT_ALL_OPS`: Select all ops from the dependency kernel libraries, register all of them into ExecuTorch runtime.
 2. `SELECT_OPS_LIST`: Only select operators from a list.
 3. `SELECT_OPS_YAML`: Only select operators from a yaml file.
+4. `SELECT_OPS_FROM_MODEL`: Only select operators from a from an exported model pte.
+5. `DTYPE_SELECTIVE_BUILD`: Enable rebuild of `portable_kernels` to use dtype selection. Currently only supported for `SELECTED_OPS_FROM_MODEL` API and `portable_kernels` lib.
 
 Other configs:
 - `MAX_KERNEL_NUM=N`: Only allocate memory for N operators.
-
-We have one more API incoming: only select from an exported model file (.pte).