Added docs entry for strtotime function

content/reference/functions/strtotime.markdown

@@ -0,0 +1,33 @@
+---
+layout: default
+title: strtotime
+aliases:
+  - "/reference-functions-strtotime.html"
+---
+
+{{< CFEngine_function_prototype(date_string) >}}
+
+**Description:** Parses a `date_string` to the number of seconds since the Epoch
+
+{{< CFEngine_function_attributes(date_string) >}}
+
+The function uses under the hood `date --date <str> +%s` from GNU coreutils, located at `/var/cfengine/bin/date`
+
+**Example:**
+
+```cf3
+bundle agent main
+{
+  vars:
+    "next_monday" int => strtotime("next Monday");
+}
+```
+
+**See also:**
+
+- Related functions
+  - [`strftime()`][strftime]
+
+**History:**
+
+- Introduced in 3.29.0