docs(stepper): update non-default boolean for editable prop (#15161)

Previously, the docs said editable can be set to true, but that is the default, so it makes more sense to say they can be set to false to change the default behavior.

Author: cbejensen

src/cdk/stepper/stepper.md

@@ -33,7 +33,7 @@ on `CdkStep` in a `linear` stepper.
 
 #### Editable step
 By default, steps are editable, which means users can return to previously completed steps and
-edit their responses. `editable="true"` can be set on `CdkStep` to change the default.
+edit their responses. `editable="false"` can be set on `CdkStep` to change the default.
 
 #### Completed step
 By default, the `completed` attribute of a step returns `true` if the step is valid (in case of

src/lib/stepper/stepper.md

@@ -127,7 +127,7 @@ on `mat-step`.
 
 #### Editable step
 By default, steps are editable, which means users can return to previously completed steps and
-edit their responses. `editable="true"` can be set on `mat-step` to change the default.
+edit their responses. `editable="false"` can be set on `mat-step` to change the default.
 
 <!-- example(stepper-editable) -->