documented availability of GPT and GPT2 models.

src/main/java/org/orekit/overview.html

@@ -276,6 +276,7 @@ discrete events. Here is a short list of the features offered by the library:</p
       <li>tropospheric refraction correction angle (Recommendation ITU-R P.834-7 and Saemundssen's formula quoted by Meeus)</li>
       <li>tropospheric model for laser ranging (Marini-Murray)</li>
       <li>Klobuchar ionospheric model (including parsing α and β coefficients from University of Bern Astronomical Institute files)</li>
+      <li>Global Pression and Temperature models (GPT and GPT2)</li>
       <li>geomagnetic field (WMM, IGRF)</li>
       <li>geoid model from any gravity field</li>
       <li>displacement of ground points due to tides</li>

src/site/markdown/index.md

@@ -245,6 +245,7 @@
     * tropospheric refraction correction angle (Recommendation ITU-R P.834-7 and Saemundssen's formula quoted by Meeus)
     * tropospheric model for laser ranging (Marini-Murray)
     * Klobuchar ionospheric model (including parsing α and β coefficients from University of Bern Astronomical Institute files)
+    * Global Pression and Temperature models (GPT and GPT2)
     * geomagnetic field (WMM, IGRF)
     * geoid model from any gravity field
     * displacement of ground points due to tides