doc: document $tmpl

doc/docs.md

@@ -3346,6 +3346,56 @@ executable, increasing your binary size, but making it more self contained
 and thus easier to distribute. In this case, `f.data()` will cause *no IO*,
 and it will always return the same data.
 
+#### $tmpl for embedding and parsing V template files
+
+V has a simple template language for text and html templates, and they can easily
+be embedded via `$tmpl('path/to/template.txt')`:
+
+
+```v ignore
+fn build() string {
+	name := 'Peter'
+	age := 25
+	numbers := [1, 2, 3]
+	return $tmpl('1.txt')
+}
+
+fn main() {
+	println(build())
+}
+```
+
+1.txt:
+
+```
+name: @name
+
+age: @age
+
+numbers: @numbers
+
+@for number in numbers
+  @number
+@end
+```
+
+output:
+
+```
+name: Peter
+
+age: 25
+
+numbers: [1, 2, 3]
+
+1
+2
+3
+```
+
+
+
+
 #### $env
 
 ```v