docs: add faq

docs/faq.rst

@@ -0,0 +1,34 @@
+Frequently Asked Questions
+==========================
+
+.. currentmodule:: senf
+
+Are there any existing users of Senf?
+    It is currently used in `Quod Libet <https://quodlibet.readthedocs.io>`__
+    and `mutagen <https://mutagen.readthedocs.io>`__.
+
+Why not use bytes for paths on Python 3 + Unix?
+    Downsides of using str: str can not be pickled as it depends on the locale
+    encoding. You have to use something like `fsn2bytes` first, or you have to
+    make sure that the encoding doesn't change across program invocations.
+
+    Upsides of using str: str has more support in the stdlib (pathlib for
+    example) and it can be used in combination with the string literal
+    ``"foo"``. The later makes ``some_fsnative + "foo"`` work for all Python
+    versions and platforms as long as it contains ASCII only.
+
+Why the weird "foo2bar" function naming?
+    As the real types depend on the platform anything like "decode"/"encode"
+    is confusing. So you end up with "a_to_b" or "a_from_b". And imo having
+    things always go one direction, being fast to parse visually and not being
+    too long makes this a good choice. But ymmv.
+
+How can it be that `fsnative()` can't fail, even with an ASCII encoding?
+    It falls back to utf-8 if encoding fails. Raising there would make
+    everything complicated and there is no good way to handle that error case
+    anyway.
+
+Why not replace ``sys.stdout`` instead of providing a new :func:`print`?
+    No monkey patching. Allows us to do our own error handling so print will
+    never fail. Printing some question marks is better than a stack trace
+    if the target is a user.

docs/index.rst

@@ -9,6 +9,7 @@
     changelog
     tutorial
     api
+    faq
 
 .. title:: Overview