README documentation out of date

[privatemaker]

Steps to reproduce

1. Read the README.md
2. Clone the repo
3. Run the command make

Expected behavior

As a new contributor to Calendar, I want to easily following instructions in the README.md file of how to start developing.

Currently, I am stuck on the first step of Build the app documentation, as the make command does not complete successfully.

Actual behaviour

After many steps make seems to complete correctly, but the make command ends with an error about about a missing phpunit.xml file.

Calendar app version

3be6085

CalDAV-clients used

No response

Browser

No response

Client operating system

No response

Server operating system

Debian 12

Nextcloud version

28

Updated from an older installed version or fresh install

fresh install

Web server error log

...

Test Suites: 60 passed, 60 total
Tests:       356 passed, 356 total
Snapshots:   25 passed, 25 total
Time:        63.094 s
Ran all test suites.
phpunit -c phpunit.xml
Could not read "phpunit.xml".
make: *** [Makefile:43: test-php] Error 1

### Log file

_No response_

### Browser log

_No response_

### Additional info

Console error log

...

Test Suites: 60 passed, 60 total
Tests: 356 passed, 356 total
Snapshots: 25 passed, 25 total
Time: 63.094 s
Ran all test suites.
phpunit -c phpunit.xml
Could not read "phpunit.xml".
make: *** [Makefile:43: test-php] Error 1

**Observations and debugging**

- Using the 2 year old `phpunit.unit.xml` fails with errors
- Running `composer run test` seems to complete successfully

[ChristophWurst]

See nextcloud/twofactor_totp#1149 as a reference. The makefile is mostly obsolete. We can recommend npm i, composer i and npm run build (or dev)