hello: Add nesting modular/shell/exercises/hello/

This gives the submodule-averse the nesting they'd usually get by
merging the master branch in a submodule at
modular/shell/exercises/hello.

diff --git a/1-Shell/hello b/modular/shell/exercises/hello/hello
similarity index 100%
rename from 1-Shell/hello
rename to modular/shell/exercises/hello/hello