[llvm] [llvm][Docs] Add a release note about the lldb DWARF indexing speedup (PR #122870)

[Pavel Labath via llvm-commits]

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@@ -449,6 +449,8 @@ Changes to LLDB
           _regexp-bt        -- Show backtrace of the current thread's call ...
           _regexp-display   -- Evaluate an expression at every stop (see 'h...
   ```
+* DWARF indexing speed (for binaries not using the debug_names index) increased
+  by 30-60%, depending on the configuration.
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labath wrote:

Done (after some wrestling with the github "edit file" UI).

https://github.com/llvm/llvm-project/pull/122870