dictionary.txt: Add nesting modular/shell/exercises/dictionary/

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

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