Add TMUX section for clipboard troubleshooting

[ekroon]

Add troubleshooting tips for clipboard tools and TMUX over SSH.

This is helping for the issue: #2773
I am not sure it is the fix, because it is unclear to me if the original problem is with TMUX too.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Related PR Found:

• PR fix(clipboard): add OSC 52 fallback for SSH/tmux environments #7028: "fix(clipboard): add OSC 52 fallback for SSH/tmux environments"
  • fix(clipboard): add OSC 52 fallback for SSH/tmux environments #7028
  • Why related: This PR directly addresses clipboard functionality in SSH/TMUX environments, which is the same issue domain as PR Add TMUX section for clipboard troubleshooting #7191. While fix(clipboard): add OSC 52 fallback for SSH/tmux environments #7028 appears to implement a code fix (OSC 52 fallback), PR Add TMUX section for clipboard troubleshooting #7191 is adding troubleshooting documentation for the same problem space. These may be complementary or one might supersede the other.

I'd recommend checking if PR #7028 already resolves issue #2773, which could affect whether the documentation in PR #7191 is still needed or should reference the fix.