doc: Add Ubuntu/Debian bat package to Readme

[maflcko]

Documentation update to fix #323

To install:

# apt-get install bat -y -q && bat /etc/os-release  
Reading package lists...
Building dependency tree...
Reading state information...
bat is already the newest version (0.11.0-2).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
───────┬────────────────────────────────────────────────────
       │ File: /etc/os-release
───────┼────────────────────────────────────────────────────
   1   │ NAME="Ubuntu"
   2   │ VERSION="19.10 (Eoan Ermine)"
   3   │ ID=ubuntu
   4   │ ID_LIKE=debian
   5   │ PRETTY_NAME="Ubuntu 19.10"
   6   │ VERSION_ID="19.10"
   7   │ HOME_URL="https://www.ubuntu.com/"
   8   │ SUPPORT_URL="https://help.ubuntu.com/"
   9   │ BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
  10   │ PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/te
       │ rms-and-policies/privacy-policy"
  11   │ VERSION_CODENAME=eoan
  12   │ UBUNTU_CODENAME=eoan
───────┴────────────────────────────────────────────────────

[sharkdp]

Thank you.