doc(ubuntu/emacs): update installation instructions

doc/make/ubuntu-12.04-detailed.md

@@ -56,7 +56,7 @@ Preparing working environment on Ubuntu 12.04
     cmake -D CMAKE_BUILD_TYPE=Release -D BOOST=ON ../src
     make
 
-### If you are using Emacs, here are some basic configurations
+### If you are using Emacs, here are some basic configurations (optional)
 
     (custom-set-variables
       '(c-basic-offset 4)
@@ -88,4 +88,4 @@ Preparing working environment on Ubuntu 12.04
         ("\\<\\(constexpr\\)\\>" . font-lock-keyword-face)
         ))
 
-You need to also set up the [Emacs Mode](../../src/emacs/README.md).
+### You need to also set up the [Emacs Mode](../../src/emacs/README.md).

src/emacs/README.md

@@ -19,8 +19,7 @@ packages, which can be installed via <kbd>M-x package-install</kbd>.
 [f]: https://github.com/rejeep/f.el
 [s]: https://github.com/magnars/s.el
 
-The following packages are *optional*, but we recommend installing them
-to use full features of ``lean-mode``.
+The following packages are optional, but strongly recommended.
 
  - [company][company]
  - [flycheck][flycheck]
@@ -81,15 +80,16 @@ Put the following code in your Emacs init file:
       (package-install p))))
 ```
 
-Then choose your installation method from the following scenarios, and
-add the corresponding code to your init file:
+Then choose your installation method from the following scenarios, and add the corresponding code to
+your init file: (note: you need to change the directory in the following code snippets to the
+directory of your clone of the repository).
 
 Case 1: Build Lean from source
 -----------------------------
 
 ```elisp
 ;; Set up lean-root path
-(setq lean-rootdir "~/projects/lean")  ;; <=== YOU NEED TO MODIFY THIS
+(setq lean-rootdir "~/projects/lean2")  ;; <=== YOU NEED TO MODIFY THIS
 (setq-local lean-emacs-path
             (concat (file-name-as-directory lean-rootdir)
                     (file-name-as-directory "src")