Mention strictPropertyInitialization requires strictNullChecks

Fix microsoft/TypeScript#23659

Author: HerringtonDarkholme

pages/Compiler Options.md

@@ -71,7 +71,7 @@ Option                                         | Type      | Default
 `--sourceRoot`                                 | `string`  |                                | Specifies the location where debugger should locate TypeScript files instead of source locations. Use this flag if the sources will be located at run-time in a different location than that at design-time. The location specified will be embedded in the sourceMap to direct the debugger where the source files will be located.
 `--strict`                                     | `boolean` | `false`                        | Enable all strict type checking options. <br/>Enabling `--strict` enables `--noImplicitAny`, `--noImplicitThis`, `--alwaysStrict`, `--strictNullChecks`, `--strictFunctionTypes` and `--strictPropertyInitialization`.
 `--strictFunctionTypes`                        | `boolean` | `false`                        | Disable bivariant parameter checking for function types.
-`--strictPropertyInitialization`               | `boolean` | `false`                        | Ensure non-undefined class properties are initialized in the constructor.
+`--strictPropertyInitialization`               | `boolean` | `false`                        | Ensure non-undefined class properties are initialized in the constructor. This option requires `--strictNullChecks` be enabled in order to take effect.
 `--strictNullChecks`                           | `boolean` | `false`                        | In strict null checking mode, the `null` and `undefined` values are not in the domain of every type and are only assignable to themselves and `any` (the one exception being that `undefined` is also assignable to `void`).
 `--stripInternal`<sup>[1]</sup>                | `boolean` | `false`                        | Do not emit declarations for code that has an `/** @internal */` JSDoc annotation.
 `--suppressExcessPropertyErrors`               | `boolean` | `false`                        | Suppress excess property checks for object literals.