fix(docs/linux): add Portal and EGL context tips

[psyke83]

Description

Add some Linux documentation to add optional configuration for Portal capture and best practices to avoid FPS throttling mostly for systems lacking Vulkan encoding support.

Screenshot

Issues Fixed or Closed

• Closes No reliable way to have valid portal token when switching display? #5400

Roadmap Issues

Type of Change

• feat: New feature (non-breaking change which adds functionality)
• fix: Bug fix (non-breaking change which fixes an issue)
• docs: Documentation only changes
• style: Changes that do not affect the meaning of the code (white-space, formatting, missing semicolons, etc.)
• refactor: Code change that neither fixes a bug nor adds a feature
• perf: Code change that improves performance
• test: Adding missing tests or correcting existing tests
• build: Changes that affect the build system or external dependencies
• ci: Changes to CI configuration files and scripts
• chore: Other changes that don't modify src or test files
• revert: Reverts a previous commit
• BREAKING CHANGE: Introduces a breaking change (can be combined with any type above)

Checklist

• Code follows the style guidelines of this project
• Code has been self-reviewed
• Code has been commented, particularly in hard-to-understand areas
• Code docstring/documentation-blocks for new or existing methods/components have been added or updated
• Unit tests have been added or updated for any new or modified functionality

AI Usage

See our AI usage policy.

• None: No AI tools were used in creating this PR
• Light: AI provided minor assistance (formatting, simple suggestions)
• Moderate: AI helped with code generation or debugging specific parts
• Heavy: AI generated most or all of the code changes

[codecov]

Bundle Report

Bundle size has no change ✅

[psyke83]

(Sorry for all the additions, I'm a bit sleep deprived and missed some obvious errors/typos that should've been caught in the first draft).

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 26.68%. Comparing base (114e633) to head (eba4d9e).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5419      +/-   ##
==========================================
- Coverage   26.68%   26.68%   -0.01%     
==========================================
  Files         111      111              
  Lines       25397    25397              
  Branches    11231    11231              
==========================================
- Hits         6777     6776       -1     
- Misses      16726    17671     +945     
+ Partials     1894      950     -944     

Flag	Coverage Δ
Archlinux	0.00% <ø> (ø)
FreeBSD-aarch64	?
FreeBSD-amd64	13.14% <ø> (-0.01%)	⬇️
Homebrew-macos-14	20.28% <ø> (+<0.01%)	⬆️
Homebrew-macos-15	20.45% <ø> (-0.02%)	⬇️
Homebrew-macos-26	20.57% <ø> (-0.03%)	⬇️
Homebrew-ubuntu-24.04	12.90% <ø> (ø)
Linux-AppImage	12.23% <ø> (ø)
Windows-AMD64	15.18% <ø> (ø)
Windows-ARM64	13.23% <ø> (ø)
macOS-arm64	17.68% <ø> (-0.01%)	⬇️
macOS-x86_64	18.36% <ø> (-0.01%)	⬇️

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see 42 files with indirect coverage changes

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