Document process for configuring clangd language server for use with tensorstore code base

[sjperkins]

• Editing tensorstore in vscode in conjunction with clangd language server is useful, especially for automatically resolving IWYU issues in #includes. The following process worked for me most recently in Add batch to VirtualChunked ReadParameters #277

1. Install bazel-compile-commands-extractor with this patch, using the WORKSPACE install method to obtain compile_commands.json
2. Then install clangd for language server functionality (dependent on compile_commands.json)
3. Add the following to .clangd

   Diagnostics: 
     UnusedIncludes: Strict
     MissingIncludes: Strict
   

The above has been quickly noted for future use. Probably a good place for it would be in the Building and Installing section of the docs.