Documentation of Gray-Scott example is incorrect

[scottwittenburg]

I'm trying to reproduce the runs described in the docs, here, but it seems that documentation is out of date.

Those docs say that we will find some scripts, config files, and a README within the install tree, under share/adios2/gray-scott, but the share/ directory no longer contains any examples (it seems it was #4722 that stopped installing examples).

If it is now required is to build the examples outside of ADIOS, then maybe it would suffice just to update the docs to point to how that can be accomplished. Or if it's possible to collect everything needed for the examples from the build tree, then perhaps that could be documented instead?

[scottwittenburg]

fyi @caitlinross