Fixed #25632 -- Documented missing version requirements for GeoDjango DB functions.

docs/ref/contrib/gis/functions.txt

@@ -197,7 +197,7 @@ Distance
 
 .. class:: Distance(expr1, expr2, spheroid=None, **extra)
 
-*Availability*: MySQL, PostGIS, Oracle, SpatiaLite
+*Availability*: MySQL (≥ 5.6.1), PostGIS, Oracle, SpatiaLite
 
 Accepts two geographic fields or expressions and returns the distance between
 them, as a :class:`~django.contrib.gis.measure.Distance` object. On MySQL, a raw
@@ -332,7 +332,7 @@ Perimeter
 
 .. class:: Perimeter(expression, **extra)
 
-*Availability*: PostGIS, Oracle, SpatiaLite
+*Availability*: PostGIS, Oracle, SpatiaLite (≥ 4.0)
 
 Accepts a single geographic field or expression and returns the perimeter of the
 geometry field as a :class:`~django.contrib.gis.measure.Distance` object. On
@@ -375,7 +375,7 @@ SnapToGrid
 
 .. class:: SnapToGrid(expression, *args, **extra)
 
-*Availability*: PostGIS, SpatiaLite
+*Availability*: PostGIS, SpatiaLite (≥ 3.1)
 
 Accepts a single geographic field or expression and returns a geometry with all
 points snapped to the given grid.  How the geometry is snapped to the grid
@@ -434,7 +434,7 @@ Union
 
 .. class:: Union(expr1, expr2, **extra)
 
-*Availability*: PostGIS, Oracle, SpatiaLite
+*Availability*: MySQL (≥ 5.6.1), PostGIS, Oracle, SpatiaLite
 
 Accepts two geographic fields or expressions and returns the union of both
 geometries.