docs: Add FAQ entry on missing symbols (#1307)

Adds FAQ entry for what to do if powerline/emoji symbols are missing.

Co-authored-by: Thomas O'Donnell <andytom@users.noreply.github.com>

docs/faq/README.md

@@ -51,3 +51,30 @@ If you get an error like "*version 'GLIBC_2.18' not found (required by starship)
 ```sh
 curl -fsSL https://starship.rs/install.sh | bash -s -- --platform unknown-linux-musl
 ```
+
+## Why don't I see a glyph symbol in my prompt?
+
+The most common cause of this is system misconfiguration. Some Linux distros in
+particular do not come with font support out-of-the-box. You need to ensure that:
+
+  - Your locale is set to a UTF-8 value, like `de_DE.UTF-8` or `ja_JP.UTF-8`. If `LC_ALL` is not a UTF-8 value, 
+    [you will need to change it](https://www.tecmint.com/set-system-locales-in-linux/).
+  - You have an emoji font installed. Most systems come with an emoji font by default, but 
+    some (notably Arch Linux) do not. You can usually install one through your system's
+    package manager--[noto emoji](https://www.google.com/get/noto/help/emoji/) is a popular choice.
+  - You are using a [powerline-patched font](https://github.com/powerline/fonts).
+
+To test your system, run the following commands in a terminal:
+
+```
+echo -e "\xf0\x9f\x90\x8d"
+echo -e "\xee\x82\xa0"
+```
+
+The first line should produce a [snake emoji](https://emojipedia.org/snake/),
+while the second should produce a [powerline branch symbol (e0a0)](https://github.com/ryanoasis/powerline-extra-symbols#glyphs).
+
+If either symbol fails to display correctly, your system is still misconfigured.
+Unfortunately, getting font configuration correct is sometimes difficult. Users
+on the Discord may be able to help. If both symbols display correctly, but
+you still don't see them in starship, [file a bug report!](https://github.com/starship/starship/issues/new/choose)