doc: add thread safety warning for process title
doc: add thread safety warning for process title

Add a small warning about uv_get_process_title()
and uv_set_process_title() not being thread safe on platforms
other than Windows. Also add a reminder for users to call
uv_setup_args() first.

Fixes: https://github.com/libuv/libuv/issues/1395
PR-URL: https://github.com/libuv/libuv/pull/1396
Reviewed-By: Saúl Ibarra Corretgé <8a7991f6950ea189abf159d6ec98d2fcc13dc5f6@gmail.com>
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <838f779c91673db29b8572ea3f54d191d3878ae2@gmail.com>

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