STYLE: clarify input requirements for extrusion models (#1181)

- changed the sectorCoeffs keyword to 'point' from 'axisPt'
  for more similarity with other dictionaries.
  Continue to accept 'axisPt' for compatibility.

tutorials/basic/overPotentialFoam/cylinder/cylinderMesh/system/extrudeMeshDict

@@ -71,9 +71,9 @@ nLayers             10;
 
 expansionRatio      1.02;
 
-sectorCoeffs
+sectorCoeffs    //<- Also used for wedge
 {
-    axisPt      (0 0.1 -0.05);
+    point       (0 0.1 -0.05);
     axis        (-1 0 0);
     angle       360;  // For nLayers=1 assume symmetry so angle/2 on each side
 }
@@ -92,14 +92,13 @@ planeCoeffs
 linearDirectionCoeffs
 {
     direction       (0 1 0);
-    thickness     0.5;
+    thickness       0.5;
 }
 
 linearRadialCoeffs
 {
     R               0.1;
-    // Optional inner radius
-    Rsurface        0.01;
+    Rsurface        0.01;  // Optional inner radius
 }
 
 radialCoeffs