[Pages] add guide for install error on Ubuntu.

Signed-off-by: Eric Wang <skygragon@gmail.com>

Author: skygragon

docs/install.md

@@ -7,10 +7,10 @@ title: Installation
 
 `node.js` (`npm` included) required, please follow the installation guide:
 
-* https://nodejs.org/en/download/package-manager/
-* https://nodejs.org/en/download/
+* [Install from package manager](https://nodejs.org/en/download/package-manager/)
+* [Install from directly download](https://nodejs.org/en/download/)
 
-You might wanna choose the latest stable release on the list.
+Please install the latest LTS version on the list above.
 
 Then verify the result:
 
@@ -23,10 +23,18 @@ Choose one of the following ways to install leetcode-cli:
 
 ### From npm
 
-This will install the latest stable release, but not include the latest development version.
+This will install the latest stable version, but not include the latest development version.
 
     $ npm install -g leetcode-cli
 
+In case Ubuntu failed due to `permission denied`, run following and try again:
+
+	$ curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.8/install.sh | bash
+	$ source ~/.bashrc
+	$ nvm install --lts
+
+See more details [here](https://docs.npmjs.com/getting-started/fixing-npm-permissions).
+
 ### From GitHub
 
 This will install the latest development version on GitHub.
@@ -35,7 +43,7 @@ This will install the latest development version on GitHub.
 
 ### From local source
 
-Similar with above, while you can introduce your changes as you like.
+Similar with above, while you can introduce your own changes as you wish.
 
     $ git clone http://github.com/skygragon/leetcode-cli
     $ cd leetcode-cli && ./bin/install