docs: update readme for Q1 2021 (#21542)

We're still working on the same set of projects for Q1 2021 as we were for Q4 2020.
The bulk of our effort is going into rolling out our MDC-based components to our users
inside Google. This is the first phase of our MDC-component rollout; the second phase
will involve moving the components to our stable npm packages.

Fixes #21538

Author: jelbourn

README.md

@@ -33,7 +33,7 @@ If you'd like to contribute, please follow our [contributing guidelines][contrib
 our [`help wanted`][help-wanted] label for a list of issues with good opportunities for
 contribution.
 
-## What we're working on now (Q4 2020):
+## What we're working on now (Q1 2021):
 * Continuing to create new, API-compatible versions of the Angular Material components backed by
 [MDC Web][] ([see @jelbourn's ng-conf talk](https://youtu.be/4EXQKP-Sihw?t=891)). Much of our effort
 is dedicated towards rolling out these new versions of the components across Angular apps