Add PHP 8.0.

Closes #11

See merge request !33

Fixes #11

Changing link to point to existing documentation for installing l10n /...

See merge request !32

Changing link to point to existing documentation for installing l10n / localisation packages in Update index.md

I left the other part until we actually cut 5.40 due to the framing

Drupal 9 link doesn't exist

See merge request !31

add note about wkhtmltopdf (aka, optional requirements for jumbo shrimp)

See merge request !30

Update index.md

See merge request !29

Remove incorrect statement about open_basedir being deprecated....

See merge request !28

CIVICRM-1707 Remove incorrect statement about open_basedir being deprecated. Safe mode was deprecated in PHP 5.3, so no longer relevant. Include minimum PHP configuration recommendations and links.

Update Requirements doc to mention that PHP7.4 is supported from MySQL 5.37 and...

See merge request !27

Update Requirements doc to mention that PHP7.4 is supported from MySQL 5.7 and also to clarify that all CMSes now supoort MySQL8 and add a note about installing on Cloud Service Providers such as AWS and Azure

Make D9 support visible

See merge request !26

This option was often set permissively in D8 project-templates - and it's
often set restrictively in D9 project-templates.

Adding the step generally shouldn't change anything for D8 admins -- and for
D9 admins it enables installation to proceed.

* This is predictably getting out of sync 'docs/drupal8'
* 'docs/drupal8' is getting updates to reference both 8+9

Update requirements.md  based on https://civicrm.org/blog/dev-team/civicrm-534-release

See merge request !25

Move the multisite installation from the SysAdmin guide

See merge request !22

Timestamp mismatch warnings link to this doc - make it more useful.

See merge request !23

Add historical PHP & MySQL compatibility info

See merge request !24