chore: heading of no-unnecessary-waiting.md (#124)

* Fix heading of no-unnecessary-waiting.md
---------

Co-authored-by: Lachlan Miller <[email protected]>

Author: openjck

README.md

@@ -73,7 +73,7 @@ Disable the `cypress/no-unnecessary-waiting` rule for the entire file by placing
 /* eslint-disable cypress/no-unnecessary-waiting */
 ```
 
-Disable the `cypress/no-unnecessary-waiting` rule for a portion of the file:
+Disable the `cypress/no-unnecessary-waiting` rule for only a portion of the file:
 
 ```js
 it('waits for a second', () => {

docs/rules/no-unnecessary-waiting.md

@@ -1,3 +1,3 @@
-## No Assigning Return Values
+## No Unnecessary Waiting
 
 See [the Cypress Best Practices guide](https://on.cypress.io/best-practices#Unnecessary-Waiting).