Docs: update console snippets
Uniformly use $ as the command prompt, and try to follow our rules at petsc.org/release/developers/documentation about when to use ..code-block:: console.
Partially addresses #1024 (closed)
Uniformly use $ as the command prompt, and try to follow our rules at petsc.org/release/developers/documentation about when to use ..code-block:: console.
Partially addresses #1024 (closed)