Add basic README (#9)

README.md

@@ -2,3 +2,37 @@
 
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+
+TZJData provides releases of the [IANA tzdata](https://www.iana.org/time-zones) compiled into the tzjfile (time zone julia file) format. The compiled data stored via [package artifacts](https://pkgdocs.julialang.org/v1/artifacts/) and used by the [TimeZones.jl] as an the source of pre-computed time zones.
+
+## Versioning
+
+The TZJData package uses [semantic versioning](https://semver.org/) like any other Julia package. Unlike most Julia packages however the TZJData package also uses build metadata to indicate the associated IANA tzdata release (e.g. TZJData release `1.0.0+2023c` uses tzdata 2023c). Each TZJData release is only associated with a single IANA tzdata release but multiple TZJData releases may correspond to the same IANA tzdata release (i.e. `1.0.0+2023c` and `1.0.1+2023c` both use tzdata 2023c).
+
+In addition to the standard semantic versioning rules used by Julia packages the TZJData package also adheres to the following internal rules: 
+
+1. The build metadata is used to indicate the tzdata version associated with each release (e.g. `2023c`)
+2. A minor release MUST be made when the tzdata version used has been updated to a newer version. A update to the tzdata version must be the immediate next release.
+3. A major release MUST be made if the tzjfile format is changed in a non-backwards compatible manner
+4. A major release MUST be used if it is desired to release older tzdata versions. In such a scenario ALL subsequent tzdata versions should be also be made into new releases to ensure the latest release in this major series is the latest tzdata.
+
+## Usage
+
+The compiled tzjfile data is stored as a series of flat files in the same way zoneinfo is on Linux distributions. Users can read this data via the [TimeZones.jl] package:
+
+```julia
+julia> using TZJData
+
+julia> using TimeZones: TZJFile
+
+julia> function load(tzname)
+ rel_path = joinpath(split(tzname, '/'))
+ return open(TZJFile.read, joinpath(TZJData.ARTIFACT_DIR, rel_path), "r")(tzname)
+ end
+load (generic function with 1 method)
+
+julia> load("Europe/Warsaw")
+(tz"Europe/Warsaw", TimeZones.Class(:STANDARD))
+```
+
+[TimeZones.jl]: https://github.com/JuliaTime/TimeZones.jl