Add more/better LLVM triples to docs

[stuxnot]

The current documentation does not give great examples for LLVM triples, which can influence nyxstones ability to assemble certain instructions, see #63.

To fix this, we should:

• Document triples for all (common) architectures
• Document that shorthand triples (like arm) might lead to failures when assembling certain instructions

[stuxnot]

Using the full LLVM triples is rather verbose. We should test how much of the triple is actually necessary and recommend using the shortest possible triple that does not impact nyxstone's assembling performance. Additionally, we are missing an example for a 32 bit arm triple.

TODO:

• For each shorthand triple, test if pc-relative instructions can be assembled
• Change the documentation to recommend the working short-hand triples
• Add examples for 32 bit arm architectures

[stuxnot]

The changes implemented by #73 seem like a step in the right direction. Using the cli description as a blueprint, we should change the documentation for the triples.