doc: add Linux GUI runtime instructions to doc/README.md #33197

  20 | @@ -21,6 +21,32 @@ Unpack the files into a directory and run:
  21 |  
  22 |  The `bitcoin` command supports subcommands like `bitcoin gui`, `bitcoin node`, and `bitcoin rpc` exposing different functionality. Subcommands can be listed with `bitcoin help`.
  23 |  
  24 | +#### Linux GUI runtime libraries
  25 | +
  26 | +If you plan to run the GUI on Linux, your system may need Qt runtime packages provided by your distribution before launching `bin/bitcoin-qt`. Package names vary by distro. Examples:
  27 | +
  28 | +- Debian/Ubuntu (Qt 6.5+ runtime):

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  20 | @@ -21,6 +21,13 @@ Unpack the files into a directory and run:
  21 |  
  22 |  The `bitcoin` command supports subcommands like `bitcoin gui`, `bitcoin node`, and `bitcoin rpc` exposing different functionality. Subcommands can be listed with `bitcoin help`.
  23 |  
  24 | +#### Linux GUI install notes
  25 | +
  26 | +- Extract the release tarball and run `bin/bitcoin-qt` as described above.
  27 | +- Depending on your distribution, additional system libraries may be required to run `bitcoin-qt`. On Debian/Ubuntu systems, you may need to install `libxcb-xinerama0` if you encounter a missing library error when launching the GUI:
  28 | +  - `sudo apt install libxcb-xinerama0`
  29 | +  - Background: `libxcb-xinerama0` has been reported as a required runtime dependency for some Ubuntu configurations when running the prebuilt binaries. See: `https://bitcoin.stackexchange.com/questions/122646/libxcb-xinerama0-library-required-by-bitcoin-qt` and related discussion in `https://github.com/bitcoin/bitcoin/issues/32097`.

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