[FEATURE] Better error message when running quantms with no input

### Description of feature

When running the simplest nextflow command with quantms, the error is quite cryptic. I believe it should point to some resources and give a useful help message in the terminal.

Example run:

```shell
% nextflow run bigbio/quantms

N E X T F L O W ~ version 25.04.7

Pulling bigbio/quantms ...
downloaded from https://github.com/bigbio/quantms.git
Launching `https://github.com/bigbio/quantms` [reverent_volhard] DSL2 - revision: e516ddca04 [master]

Downloading plugin nf-schema@2.4.2
ERROR ~ Argument of `file` function cannot be null

-- Check script '.nextflow/assets/bigbio/quantms/workflows/quantms.nf' at line: 45 or see '.nextflow.log' file for more details
```