Restore deleted TICON readme

Author: bkeepers

data/ticon/README.md

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+# TICON-4 Tide Station Data
+
+[TICON-4](https://www.seanoe.org/data/00980/109129/) is a global dataset of tidal harmonic constituents derived from the **GESLA-4** (Global Extreme Sea Level Analysis v.4) sea-level gauge compilation. It provides tidal characteristics for  **4,264 tide stations** worldwide, with emphasis on global coverage outside the United States (which is covered by NOAA's tide database).
+
+**Key Details:**
+- **Source:** [TICON-4 @ SEANOE](https://www.seanoe.org/data/00980/109129/)
+- **Manual:** [TICON Documentation](https://www.seanoe.org/data/00980/109129/data/122852.pdf)
+- **License:** CC-BY-4.0 (Creative Commons Attribution 4.0)
+- **Coverage:** Global tide stations with harmonic constituent analysis from GESLA-4 observations
+
+Each station in this dataset contains harmonic constituents (amplitude and phase for tidal frequency components such as M2, K1, O1, etc.) extracted from historical sea-level records.
+
+![](https://www.seanoe.org/data/00980/109129/illustration.jpg)
+
+## Synthetic Tidal Datums
+
+TICON-4 does not provide empirically derived tidal datums. Instead, this dataset includes **synthetic tidal datums** computed from 19-year harmonic predictions using the harmonic constituents, not from observed water level data. This approach generates theoretical datums that represent long-term average tidal characteristics without the influence of weather events, non-tidal water level changes, or observational gaps.
+
+These datums should eventually be replaced with water-level-derived datums when available. See [#40](https://github.com/neaps/tide-database/issues/40).
+
+## References
+
+- [TICON-4 Dataset](https://www.seanoe.org/data/00980/109129/)
+- [TICON Manual](https://www.seanoe.org/data/00980/109129/data/122852.pdf)
+- [GESLA-4 Project](https://gesla787883612.wordpress.com)