title: `mkcert` command not found, after installing ddev
body: <p><code>mkcert</code> doesn't seem to be installed (or maybe not in the right path) on Ubuntu</p>
  
  <pre><code>ddev version
  DDEV-Local version  v1.8.0                        
  commit              v1.8.0                        
  db                  drud/ddev-dbserver:v1.8.0-10.2
  dba                 drud/phpmyadmin:v1.8.0        
  ddev-ssh-agent      drud/ddev-ssh-agent:v1.8.0    
  docker              18.09.5                       
  docker-compose      1.21.2                        
  domain              ddev.local                    
  os                  linux                         
  router              drud/ddev-router:v1.8.0       
  web                 drud/ddev-webserver:v1.8.0 
  </code></pre>
  
  <p>On Ubuntu 18</p>
  
  <pre><code>mkcert -install
  zsh: command not found: mkcert
  </code></pre>