Document prompt_pwd

Fixes #253

doc_src/prompt_pwd.txt

@@ -0,0 +1,28 @@
+\section prompt_pwd prompt_pwd - Print pwd suitable for prompt
+
+\subsection prompt_pwd-synopsis Synopsis
+\fish{synopsis}
+prompt_pwd
+\endfish
+
+\subsection prompt_pwd-description Description
+
+prompt_pwd is a function to print the current working directory in a way suitable for prompts. It will replace the home directory with "~" and shorten every path component but the last to a default of one character.
+
+To change the number of characters per path component, set $fish_prompt_pwd_dir_length to the number of characters. Setting it to 0 or an invalid value will disable shortening entirely.
+
+\subsection prompt_pwd-example Examples
+
+\fish
+>_ cd ~/
+>_ echo $PWD
+/home/alfa
+>_ prompt_pwd
+~
+>_ cd /tmp/banana/sausage/with/mustard
+>_ prompt_pwd
+/t/b/s/w/mustard
+>_ set -g fish_prompt_pwd_dir_length 3
+>_ prompt_pwd
+/tmp/ban/sau/wit/mustard
+\endfish

share/functions/prompt_pwd.fish

@@ -1,4 +1,10 @@
 function prompt_pwd --description "Print the current working directory, shortened to fit the prompt"
+	set -q argv[1]; and switch $argv[1]
+		case -h --help
+			__fish_print_help prompt_pwd
+			return 0
+	end
+
 	# This allows overriding fish_prompt_pwd_dir_length from the outside (global or universal) without leaking it
 	set -q fish_prompt_pwd_dir_length; or set -l fish_prompt_pwd_dir_length 1