Docs: Create a new tutorial for first-time users

[mbercx]

Create a short (~30 min) tutorial to give beginning users a first introduction on how to use AiiDA.

[giovannipizzi]

Here a possible short code that can be used as CalcJob, avoiding to have to create a custom plugin.

1. Make sure they start with a localhost computer (probably with direct scheduler and local transport)

2. Ask them to setup a bash@localhost code (good excuse to explain what a code is), with the following one-liner:

   verdi code setup -L bash -P templatereplacer --on-computer --computer=localhost --remote-abs-path=/bin/bash --non-interactive

   Optionally, you can explain them verdi code list here.

3. Ask them to run a calculation with the following script:

   from aiida.orm import Dict, load_code
   from aiida.engine import run_get_node
   
   code = load_code('bash@localhost')
   
   builder = code.get_builder()
   builder.parameters = Dict(dict={'x': 3, 'y': 4})
   builder.template = Dict(
       dict={
           'input_file_name': 'script.sh',
           'input_file_template': "echo $(({x} * {y}))",
           'cmdline_params': ['script.sh'],
           'output_file_name': 'stdout.txt'
       }
   )
   builder.metadata.options = {
       'resources': {'num_machines': 1},
       'parser_name': 'templatereplacer.doubler',
   }
   
   results, calcjobnode = run_get_node(builder)
   
   print(calcjobnode.res.value)

Possible things to adapt:

• define a better parser (e.g. generic.integer_parser, generic.cvs_parser, generic.json_parser) that could become part of AiiDA
• use print(results['output_parameters'].get_dict()['value']) instead of calcjobnode.res.value (a bit more explicit, but maybe they understand what is going on.
• should we extend the template_replacer so that if an input_file_template is provided, the input_file_name is set by default (maybe using the metadata option that now AiiDA has), and also the cmdline_params becomes by default just the filename? This would remove two lines from above

We should then think if instead of multiplying two numbers we want to do something more fancy, but the snippet above should be enough to extend the example.

Note also that the advantage of the input parameters dict is that the values can then be queried.
And, even if slightly more complex than the add calculation, this makes it obvious how this can be extended to any code without the need to write any new calculation plugin.