DSDE-198: docs(era5): readme file

[EstebanMontandon]

I just created this PR for the purpose of adding my quick review of the ERA5 docs.

[EstebanMontandon]

In the section Suported variables would be handy to add a link to the toolbox documentation :

[EstebanMontandon]

I just saw that in the code we have:

@parameter(
    "variable",
    name="Variable",
    type=str,
    choices=[
    	"10 metre U wind component",
    	"10 metre V wind component",
    	"2 metre temperature",
    	"Total precipitation",
    	"Volumetric soil water layer 11",
]

perhaps we need to update this?

[EstebanMontandon]

I would just add a screenshot with the pipelines parameters filled in as an example... just to keep the same style as other readme files I've seen ;)

[EstebanMontandon]

Additional comments:
Overall the descriptions of the functionality is clear and readable (more than enough for people with the correct background I think).

I just had a couple of doubts:

1. In the case of ERA5 Import DHIS2 Pipeline
   How do you handle the ‘Append’ option? “ Do you make a request for those dataElements and compare dates?

2. ERA5-Land to DHIS2 Import Pipeline & ERA5-Land Data Synchronization Pipeline
   These two ERA5-Land* pipelines are intended to replace the previous ERA5 implementation of extract->aggregate->import? I have the impression that these two pipelines cover the general use cases correct?

[lgarridobsq]

Holi, I change the name because I wanted to see if I could link it to the JIRA issue this way -- it worked ⭐ remember that doing it by including the jira code in the branch name also works
I let Yann review the PR