chore: add .gitattributes

[rkrasiuk]

Description

Add .gitattributes to ignore the language in contents of assets/ and documentation/ folders.

[github-actions]

Valgrind Results:

==4107== Cachegrind, a cache and branch-prediction profiler
==4107== Copyright (C) 2002-2017, and GNU GPL'd, by Nicholas Nethercote et al.
==4107== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==4107== Command: target/release/snailtracer
==4107== 
--4107-- warning: L3 cache found, using its data for the LL simulation.
Running snailtracer example!
elapsed: 1.882236975s
==4107== 
==4107== I   refs:      427,439,026
==4107== I1  misses:          3,171
==4107== LLi misses:          2,854
==4107== I1  miss rate:        0.00%
==4107== LLi miss rate:        0.00%
==4107== 
==4107== D   refs:      203,986,857  (132,175,935 rd   + 71,810,922 wr)
==4107== D1  misses:        342,748  (    202,811 rd   +    139,937 wr)
==4107== LLd misses:        137,711  (      4,396 rd   +    133,315 wr)
==4107== D1  miss rate:         0.2% (        0.2%     +        0.2%  )
==4107== LLd miss rate:         0.1% (        0.0%     +        0.2%  )
==4107== 
==4107== LL refs:           345,919  (    205,982 rd   +    139,937 wr)
==4107== LL misses:         140,565  (      7,250 rd   +    133,315 wr)
==4107== LL miss rate:          0.0% (        0.0%     +        0.2%  )