Added text regarding patch issues during installation

[mt-satak]

Why did I submit this PR?

When performing composer install, the patch to hoa/protocol failed to apply.

  - Applying patches for hoa/protocol
    patches/Node.patch (0)
   Could not apply patch! Skipping. The error was: The process "patch '-p1' --no-backup-if-mismatch -d '/Users/satak/dev/phpstan-src/vendor/hoa/protocol' < '/Users/satak/dev/phpstan-src/patches/Node.patch'" exceeded the timeout of 300 seconds.

In Patches.php line 331:
                                              
  Cannot apply patch 0 (patches/Node.patch)! 

This error is caused by an out-of-date version of patch pre-installed on macOS, and can be resolved by doing brew install gpatch before running composer install to bring it up to date.

Purpose of this PR

To add the above solution to the README to leave a clue for solving similar errors when they occur.

[phpstan-bot]

You've opened the pull request against the latest branch 1.11.x. If your code is relevant on 1.10.x and you want it to be released sooner, please rebase your pull request and change its target to 1.10.x.

[ondrejmirtes]

Thank you.