scaffold the CLI, logging and turn research into TODOs

TODO.md

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+# Subcommands
+
+## import
+Import an identity from a gpg key.
+
+Relevant crates:
+```Cargo.toml
+# For finding the cache directory in which to store the SSH keys exported from GPG and identities
+dirs = "6.0.0"
+# For importing GPG keys
+gpgme = "0.11.0"
+
+# For reading/writing identities' files
+serde = { version = "1.0.228", features = ["derive"] }
+toml = "0.9.11"
+```
+
+## use
+Set the identity of the current git repo
+
+Relevant crates:
+```Cargo.toml
+# For writing to the local git config as well as to allow configuring git-identity from git
+git2 = { version = "0.20.3", default-features = false }
+```
+
+## show
+Show a saved identity or the identity that's currently effective
+
+## delete
+Remove a saved identity
+
+## list
+List all saved identities
+
+## edit
+Interactively edit a saved identity (or in a text editor when using a specific flag)
+
+# User input
+[inquire](https://docs.rs/inquire/latest/inquire/) seems simple enough. But
+[dialoguer](https://docs.rs/dialoguer/latest/dialoguer/) is the one use by tauri which seems much
+more complete.
+
+# Completions
+clap_complete does that statically. It will be able to do it dynamically once the
+[Rust-Native Completion Engine (#3166)](https://github.com/clap-rs/clap/issues/3166) feature lands