add jenkin guide

server/jenkins_guide.md

+## Jenkins Setup Guide
+
+Target server: CenOS 6.6
+Jenkins version: 1.607
+
+
+### 1. Set up server
+
+1.1. Install essensial build tools
+
+```bash
+sudo yum groupinstall "Development tools"
+```
+
+1.2. Install rbenv to Jenkins's home(/var/lib/jenkins)
+
+```bash
+git clone https://github.com/sstephenson/rbenv.git .rbenv
+```
+
+1.3. Install ruby-builds plugin
+
+```bash
+git clone https://github.com/sstephenson/ruby-build.git .rbenv/plugins/ruby-build
+```
+
+1.4. Config `.bashrc` file
+
+```bash
+echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
+echo 'eval "$(rbenv init -)"' >> ~/.bashrc
+```
+
+### 2. Setup Jenkins
+
+2.1. From the root page, click “Manage Jenkins” then “Manage Plugins”. From the “Available” tab, check the following plugins:
+
+  - rbenv
+  
+2.2. Select “Download now and install after restart”
+
+### 3. Setup Project
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