Fix video not playing on systems with no `python` binary

[Silejonu]

Debian 11 and Ubuntu 22.04 use python3 as their Python 3 binary. python is reserved for Python 2, and is not installed by default.

This commit checks if the python binary exists on the system, and if not, uses python3 instead.

Fixes #40

[tresf]

Tested, fixes playback on MacOS Ventura (and probably many others).

[mattpopovich]

Please merge!! :smiling_imp:

[DAcodedBEAT]

similar changesets:

• https://github.com/CryptoDragonLady/rickrollrc/pull/3
• https://github.com/keroserene/rickrollrc/pull/37