Document Sketcher constraint double-click rename

[zacharyhu]

Summary:

• Clarify that double-clicking a dimensional constraint in the Sketcher constraint list edits its value.
• Document that, in FreeCAD 1.2, double-clicking a geometric constraint in the list renames it.

Source:

• Sketcher: Double click geometric constraint trigger rename. FreeCAD/FreeCAD#27678

Verification:

• git diff --check -- wiki/Sketcher_Dialog.wikitext

Refs #94

[Reqrefusion]

This doesn't seem like a very good change.