Add extra text to help users link modifications to inputs

[charlotte]

testers: CERFACS (marie-pierre)
type: confusing
location: Simulation/Model? Tab: Needed Inputs
location: Simulation Tab: Describe Ensemble: Input Modifications

not easy to understand the link between these concept, f.e. that an "Input Modification" are relative to a "Needed input" (and not to a "Resolve Input")

[charlotte]

I think part of the problem here is that we use the word "input" in different contexts.
We use it to describe input variables
We use it to describe input modifications
We also use it to say that inputs are needed

Need to think of how we can distinugish these concepts more clearly

[charlotte]

Will be fixed by #513

[charlotte]

Collecting helpful text Defining a "Needed Input" and "Resolve"-ing it are 2 prerequisites before establishing a Conformance