Added `Available Memory` module to Linux

[Ace-Krypton]

I only added Linux for now, I don't have windows laptop on me right now so I will add it later on

[lfreist]

Adding only Linux is fine, but please implement dummy methods for all platforms just returning a default value (-1 for integer types) so that all platforms can build (see github actions). Thanks for your contribution!

[Ace-Krypton]

I added dummy methods, if there is something else wrong sorry, I am not good at this kinda styling, just tried to help with something :)

[lfreist]

You just returned a string from a function that must return an integer. Please return -1 instead of "" and it is fine.

Thanks for your efforts!

[Ace-Krypton]

last one should be okay, anyways thanks, I will fill out those dummy methods too, in few weeks