Add Times-scripts/FC_GetWeekNumber_readme.md

Times-scripts/FC_GetWeekNumber_readme.md

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+# FC_GetWeekNumber
+
+## Description
+Calculates the **ISO 8601 week number** (week 1 = week containing first Thursday)  
+Input: DT (DATE_AND_TIME)  
+Output: UINT (1..53)
+
+## Features
+- Follows ISO 8601 rules (Monday week start)
+- Uses built-in Siemens functions (WEEKDAY, DAY_OF_YEAR)
+
+## Input / Output
+**Input**
+- `stDateTime` : DT     Date/time value
+
+**Return**
+- UINT                  Week number 1..53
+
+## Usage example
+```iecst
+wCurrentWeek := "FC_GetWeekNumber"(stDateTime := #Now);
+IF wCurrentWeek = 1 THEN
+    // New year logic...
+END_IF;