Fix: add fish completions for forgit diff and forgit show (#434)

Author: sandr01d

completions/git-forgit.fish

@@ -52,11 +52,13 @@ complete -c git-forgit -n '__fish_seen_subcommand_from checkout_file' -a "(__fis
 complete -c git-forgit -n '__fish_seen_subcommand_from checkout_tag' -a "(__fish_git_tags)" -d Tag
 complete -c git-forgit -n '__fish_seen_subcommand_from cherry_pick' -a "(complete -C 'git cherry-pick ')"
 complete -c git-forgit -n '__fish_seen_subcommand_from clean' -a "(__fish_git_files untracked ignored)"
+complete -c git-forgit -n '__fish_seen_subcommand_from diff' -a "(complete -C 'git diff ')"
 complete -c git-forgit -n '__fish_seen_subcommand_from fixup' -a "(__fish_git_local_branches)"
 complete -c git-forgit -n '__fish_seen_subcommand_from log' -a "(complete -C 'git log ')"
 complete -c git-forgit -n '__fish_seen_subcommand_from reflog' -a "(complete -C 'git reflog ')"
 complete -c git-forgit -n '__fish_seen_subcommand_from rebase' -a "(complete -C 'git rebase ')"
 complete -c git-forgit -n '__fish_seen_subcommand_from reset_head' -a "(__fish_git_files all-staged)"
 complete -c git-forgit -n '__fish_seen_subcommand_from revert_commit' -a "(__fish_git_commits)"
+complete -c git-forgit -n '__fish_seen_subcommand_from show' -a "(complete -C 'git show ')"
 complete -c git-forgit -n '__fish_seen_subcommand_from stash_show' -a "(__fish_git_complete_stashes)"
 complete -c git-forgit -n '__fish_seen_subcommand_from stash_push' -a "(__fish_git_files modified deleted modified-staged-deleted)"