update haskell README

Improve PATH section. As requested in #2142.

Also make some minor improvements.

layers/+lang/haskell/README.org

@@ -22,9 +22,9 @@
    - [[#cabal-commands][Cabal commands]]
    - [[#cabal-files][Cabal files]]
  - [[#faq][FAQ]]
-   - [[#repl-doesnt-work][REPL doesn't work.]]
+   - [[#repl-doesnt-work][REPL doesn't work]]
-   - [[#i-am-using-stack-and-ghc-mod-but-ghc-mod-doesnt-work][I am using =stack= and =ghc-mod=, but =ghc-mod= doesn't work.]]
+   - [[#i-am-using-stack-and-ghc-mod-but-ghc-mod-doesnt-work][I am using =stack= and =ghc-mod=, but =ghc-mod= doesn't work]]
-   - [[#repl-is-stuck][REPL is stuck.]]
+   - [[#repl-is-stuck][REPL is stuck]]
 
 * Description
 This layer adds support for the [[https://www.haskell.org/][Haskell]] language.
@@ -36,7 +36,6 @@ This layer adds support for the [[https://www.haskell.org/][Haskell]] language.
 *This layer is in construction, it needs your contributions and bug reports.*
 
 * Install
-
 ** Layer
 To use this contribution add it to your =~/.spacemacs=
 
@@ -64,14 +63,35 @@ following command:
 #+END_SRC
 
 ** Setup PATH
+First of all make sure that your =$PATH= contains installation path for Haskell
+tools like =ghc=, =ghci= etc. It depends on how you have installed =ghc=. But
+you can always check it by calling =$ which ghc= in your terminal. =Stack= users
+should add only installation path of =stack= itself, usually it's
+=~/.local/bin=.
 
-Make sure that your =$PATH= contains installation path for =cabal= packages. If
+Then make sure that your =$PATH= contains installation path for =cabal=
-you are using =cabal= it should be =~/.cabal/bin= or
+packages. If you are using =cabal= it should be =~/.cabal/bin= or
-=/Users/<username>/Library/Haskell/bin= (for Haskell for Mac users). If you are
+=/Users/<username>/Library/Haskell/bin= (for 'Haskell for Mac' users). If you
-using =stack= then it should be =~/.local/bin=. So if this path is not in
+are using =stack= then it should be =~/.local/bin=.
-=$PATH=, just add it and Spacemacs will automatically pick up shell =$PATH=.
 
-_Alternatively_, you can add it to the Emacs =exec-path= variable in the
+If you are using =bash=, =sh= or =zsh=, you could update your =$PATH= by using
+following command:
+
+#+BEGIN_SRC sh
+  $ export PATH=~/.local/bin:$PATH
+#+END_SRC
+
+If you are using =fish=, you could update your =$PATH= by using following
+command:
+
+#+BEGIN_SRC fish
+  $ set -x PATH ~/.local/bin $PATH
+#+END_SRC
+
+After you setup your =$PATH=, emacs should automatically pick it's value (after
+restart).
+
+_Alternatively_, you can add path to the Emacs =exec-path= variable in the
 =dotspacemacs/user-config= function of your =.spacemacs= file:
 
 #+BEGIN_SRC emacs-lisp
@@ -270,8 +290,7 @@ This commands are available in a cabal file.
 
 * FAQ
 
-** REPL doesn't work.
+** REPL doesn't work
-
 Usually =haskell-mode= is great at figuring out which interactive process to
 bring up. But if you are experiencing problems with it you can help
 =haskell-mode= by setting =haskell-process-type= as in following code:
@@ -289,13 +308,11 @@ Available options are:
 - cabal-ghci
 - stack-ghci
 
-** I am using =stack= and =ghc-mod=, but =ghc-mod= doesn't work.
+** I am using =stack= and =ghc-mod=, but =ghc-mod= doesn't work
-
 Make sure that =dist= directory doesn't exist in your project root. So if it
 exists, just remove it and try again.
 
-** REPL is stuck.
+** REPL is stuck
-
 Make sure that when you are typing anything in REPL there is a space between
-what you type and =λ=. This problem usually happens when you switch from normal
+what you type and =λ>=. This problem usually happens when you switch from normal
-mode to edit mode.
+mode to insert mode.