wp-now: Refresh the Known Issues list for WCEU (WordPress#68)

See WordPress/playground-tools#28

## What?

Refreshes the Known Issues list in preparation for WCEU

## Why?

It's helpful to give new users some heads up about the more obvious
issues we already know about.

packages/wp-now/README.md

@@ -68,9 +68,12 @@ Of these, `wp-now php` currently supports the `--path=<path>` and `--php=<versio
 ## Known Issues
 
 -   Running `wp-now start` in 'wp-content' or 'wordpress' mode will produce some empty directories: [WordPress/wordpress-playground#328](https://github.com/WordPress/wordpress-playground/issues/328)
+-   Inline images are broken when site starts on a different port: [WordPress/wordpress-playground#356](https://github.com/WordPress/wordpress-playground/issues/356)
+-   `wp-now` doesn't build or start on Windows: [WordPress/playground-tools#66](https://github.com/WordPress/playground-tools/issues/66), [WordPress/playground-tools#11](https://github.com/WordPress/playground-tools/issues/11)
+-   Pretty permalinks aren't yet supported: [WordPress/playground-tools#53](https://github.com/WordPress/playground-tools/issues/53)
+-   It's not possible to set `WP_DEBUG` and other `wp-config.php` constants: [WordPress/playground-tools#17](https://github.com/WordPress/playground-tools/issues/17)
 -   In 'wordpress' mode, `wp-now` can connect to a MySQL database with `define( 'DB_HOST', '127.0.0.1' );`, but `define( 'DB_HOST', 'localhost' );` does not work: [WordPress/wordpress-playground#369](https://github.com/WordPress/wordpress-playground/issues/369)
 -   `wp-now` published versions can appear random: [WordPress/wordpress-playground#357](https://github.com/WordPress/wordpress-playground/issues/357)
--   Inline images are broken when site starts on a different port: [WordPress/wordpress-playground#356](https://github.com/WordPress/wordpress-playground/issues/356)
 
 ## Comparisons