Missing document on detailed clang-tidy checks enabled by default / disabled

[zwuis]

It's just mentioned that "Not all checks work within clangd.", which is not clear enough and may confuse users (clangd/clangd#759). These tests should be listed.

Current document and disabled checks:

clangd-www/features.md

Lines 41 to 42 in a3b06b5

	clangd respects your project's `.clang-tidy` file which controls the checks to
	run. Not all checks work within clangd.

https://github.com/llvm/llvm-project/blob/75ad8b23c0f430bcf3a783c50ef53b926147dff7/clang-tools-extra/clangd/TidyProvider.cpp#L197-L224

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Some clang-tidy checks are enabled when there is no configuration in ".clangd" and ".clang-tidy" files (I tested with clangd 18.1.8 but didn't check the source code). I think it can be documented.

Checks enabled by default:

https://github.com/llvm/llvm-project/blob/75ad8b23c0f430bcf3a783c50ef53b926147dff7/clang-tools-extra/clangd/TidyProvider.cpp#L170-L185