docs: add `patch-package` reference to Customization section

[agilgur5]

Description

• for when you need to make some small changes to the internal code and forking is a bit too extreme of an option

  • hopefully patch-package means folks get their changes in faster without waiting for PRs and means folks don't have to use outdated forks etc

• it was first recommended by Shawn in issues then strongly recommended by Jared and I've recommended it a few times too for smaller changes

  • Quoting Jared: "Yes, to documenting patch-package as ultimate escape hatch"

Tags

Referenced in:

• https://github.com/formium/tsdx/issues/110#issuecomment-518079299
• https://github.com/formium/tsdx/issues/389#issuecomment-568785862
• https://github.com/formium/tsdx/pull/436#issuecomment-578239297
• https://github.com/formium/tsdx/issues/509#issuecomment-586663005
• https://github.com/formium/tsdx/issues/656#issuecomment-612704650
• https://github.com/formium/tsdx/pull/669#issuecomment-612709831
• https://github.com/formium/tsdx/issues/744#issuecomment-643025596
• https://github.com/formium/tsdx/pull/811#discussion_r479410046
• https://github.com/formium/tsdx/issues/852#issuecomment-688420672

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