sway.5.scd: clarify workspace config commands

This clarifies that `workspace <name> output <outputs...>` and
`workspace <name> gaps ...` do not operate on existing workspaces.
Additionally, alternate commands/solutions that operate on existing
workspaces are listed.

sway/sway.5.scd

@@ -699,6 +699,9 @@ The default colors are:
 	Specifies that workspace _name_ should have the given gaps settings when it
 	is created.
 
+	This command does not affect existing workspaces. To alter the gaps of an
+	existing workspace, use the _gaps_ command.
+
 *workspace* <name> output <outputs...>
 	Specifies that workspace _name_ should be shown on the specified _outputs_.
 	Multiple outputs can be listed and the first available will be used. If the
@@ -706,6 +709,11 @@ The default colors are:
 	is higher on the list becomes available, the workspace will be move to the
 	higher priority output.
 
+	This command does not affect existing workspaces. To move an existing
+	workspace, use the _move_ command in combination with the _workspace_
+	criteria (non-empty workspaces only) or _workspace_ command (to switch
+	to the workspace before moving).
+
 *workspace_auto_back_and_forth* yes|no
 	When _yes_, repeating a workspace switch command will switch back to the
 	prior workspace. For example, if you are currently on workspace 1,