update documentation

.gitignore

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+.DS_Store
+
 # ---> Rust
 # Generated by Cargo
 # will have compiled files and executables

README.md

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 # Team Time Zones
+
+A simple CLI app for displaying rich 24 hour time information for multiple
+people or locations.
+
+![Screenshot of a terminal window running the Team Time Zones TUI. The main
+feature is a table displaying a list of locations across the top including
+"Oakland", "UTC", and "Pacific Standard Time", each heading up a column of 24
+cells displaying relative times throughout the day in the corresponding time
+zone. Standard 9 to 5 working hours are highlighted in brighter text, and the
+row representing the current hour is rendered in red. An input hint at the
+bottom reads "Filter" with a slash and "Quit" with a Q.](./docs/screenshot.png)
+
+## Install
+
+```sh
+# Install Rust toolchain
+mise install
+# Build executable
+cargo build --release
+# Move to path (substitute any destination in your $PATH)
+cp target/release/ttz /usr/local/bin
+```
+
+## Run
+
+With example config:
+
+```sh
+ttz -c ./ttz.example.kdl
+```
+
+Or create a `~/.config/ttz.kdl` to be loaded automatically. Refer to
+`ttz --help` for more information.
+
+## Configuration
+
+TTZ uses the [KDL](https://kdl.dev/) format, with the following schema repeated
+for each desired location:
+
+```kdl
+location "<DISPLAY NAME>" tz="<IANA TIME ZONE NAME>"
+```
+
+For valid time zone names, refer to the
+[chrono_tz docs](https://docs.rs/chrono-tz/latest/chrono_tz/enum.Tz.html),
+[Wikipedia](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones), or
+the [IANA database](https://www.iana.org/time-zones).
+
+Time zone names are case-sensitive.

ttz.example.kdl

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 location Oakland tz="America/Los_Angeles"
 location UTC tz="UTC"
-// Unclear why this is +8 and not -8.
+// Etc/GMT* have their signs intentionally reversed for POSIX compliance.
 location "Pacific Standard Time" tz="Etc/GMT+8"