add initial bash_completion script

bash_completion.d/trezorctl.sh

@@ -0,0 +1,14 @@
+_trezorctl()
+{
+    local cur prev cmds base
+    COMPREPLY=()
+    cur="${COMP_WORDS[COMP_CWORD]}"
+    prev="${COMP_WORDS[COMP_CWORD-1]}"
+
+    cmds=$(trezorctl --help | grep -A 1 'Available commands:' | tail -n 1 | tr '{},' '   ')
+
+    COMPREPLY=($(compgen -W "${cmds}" -- ${cur}))
+    return 0
+}
+
+complete -F _trezorctl trezorctl