[Docs] Add a note about fish-related problems

See #1668 for more details.

Author: bbatsov

README.md

@@ -109,6 +109,7 @@ See the [online documentation](https://docs.projectile.mx) for more details.
 
 * Some operations like search (grep) depend (presently) on external
   utilities such as `find`.
+* Commands depending on external utilities might misbehave on the `fish` shell.
 * Using Projectile over TRAMP might be slow in certain cases.
 * Some commands might misbehave on complex project setups (e.g. a git project with submodules)
 * Projectile was mostly tested on Unix OS-es (e.g. GNU/Linux and macOS), so some functionality might not work well on Windows

doc/modules/ROOT/pages/troubleshooting.adoc

@@ -61,3 +61,14 @@ least what's being required).
 
 Emacs doesn't load the new files, it only installs them on disk.  To see the
 effect of changes you have to restart Emacs.
+
+=== Some commands not working properly with the fish shell
+
+I'm not sure what's causing this (likely different quoting rules), but it's easy to fix it:
+
+[source,elisp]
+----
+(setq shell-file-name "/bin/bash")
+----
+
+In general, I've noticed that Emacs doesn't play very well with fish.