fish: standardize config structure

config/shell/.config/fish/conf.d/50-prompt.fish

@@ -0,0 +1,12 @@
+function fish_prompt -d "Write out the prompt"
+    # This shows up as USER@HOST /home/user/ >, with the directory colored
+    # $USER and $hostname are set by fish, so you can just use them
+    # instead of using `whoami` and `hostname`
+    printf '%s@%s %s%s%s > ' $USER $hostname \
+        (set_color $fish_color_cwd) (prompt_pwd) (set_color normal)
+end
+
+# oh-my-posh
+if test -f $HOME/.config/posh_theme.omp.json; and type -q oh-my-posh
+    oh-my-posh init fish --config $HOME/.config/posh_theme.omp.json | source
+end