Add note about php xml extension requirement to getting started guide

[wayward777]

Upon fresh install, I ran into same issue as reported in #500 & #315. Turns out, it was missing xml extension which is not mentioned in the installation docs. May want to add a note to the system requirements section.

$ vendor/bin/jigsaw init blog
...
Installation failed, reverting ./composer.json and ./composer.lock to their original content.
The 'tightenco/jigsaw-blog-template' preset could not be found.

Full error message here

$ vendor/bin/jigsaw init blog
...
...
  Problem 1
    - Root composer.json requires tightenco/jigsaw-blog-template * -> satisfiable by tightenco/jigsaw-blog-template[v1.0.0, ..., v1.4.1].
    - samdark/sitemap[2.2.0, ..., 2.4.1] require ext-xmlwriter * -> it is missing from your system. Install or enable PHP's xmlwriter extension.
    - tightenco/jigsaw-blog-template v1.0.0 requires tightenco/jigsaw dev-master -> found tightenco/jigsaw[dev-nd/fix-escaping-in-markdown-to-preserve-phpdoc-annotations-like-inheritdoc, dev-gc/fixes-once-directive, dev-gc/onboard-duster, dev-dependabot/npm_and_yarn/stubs/site/vite-6.4.1, dev-jbk/kernel, dev-jbk/blade-files-no-extend, dev-main, dev-ci, v0.1.0, ..., v0.6.4, v1.0.0, ..., v1.8.3] but it does not match the constraint. Perhaps dev-master was renamed to dev-main?
    - tightenco/jigsaw-blog-template[v1.0.1, ..., v1.1.2] require samdark/sitemap ^2.2 -> satisfiable by samdark/sitemap[2.2.0, ..., 2.4.1].
    - tightenco/jigsaw-blog-template[v1.2.0, ..., v1.2.3] require samdark/sitemap ^2.2.1 -> satisfiable by samdark/sitemap[2.2.1, 2.3.0, 2.4.0, 2.4.1].
    - tightenco/jigsaw-blog-template[v1.3.0, ..., v1.4.1] require tightenco/jigsaw ^1.6 -> found tightenco/jigsaw[v1.6.0, ..., v1.8.3] but the package is fixed to v1.3.40 (lock file version) by a partial update and that version does not match. Make sure you list it as an argument for the update command.
...
...
Installation failed, reverting ./composer.json and ./composer.lock to their original content.
The 'tightenco/jigsaw-blog-template' preset could not be found.

It may be that my distro disables this extension, as the php docs state the xml extension is enabled by default. I had to sudo apt install php-xml in order to use templates with jigsaw. Not sure if this is common as I'm new to the php world.

Following the guide verbatim and attempting to init a project with any template will fail without this extension.

[tomasnorre]

The https://github.com/samdark/sitemap/blob/master/composer.json states the requirement, which triggers the information you posted. This is how composer works as a package manager.

The idea of having additional installation instructions, makes it harder to maintain. Let's say that the samdark/sitemap requires a new package tomorrow, then the Installation steps of Jigsaw would need to be updated, I could also be that this package is dropped, then the installation steps would need to be updated too. Composer tells you want it needs.

This way as it is today, and which I find correctly, it is more organic and fluid.