Contributing guidelines: REST API information links and spelling fixes

CONTRIBUTING.md

-Welcome! Any kinds of contributions are very welcomed. Please go through our contribution
-guide before you try to create a Pull Request for `jcli`.
+Welcome! Any kinds of contributions are very welcome. Please go through our contribution
+guide before you create a Pull Request for `jcli`.
 
 ## CLI
 
 `jcli` is a command line interface. So a CLI framework is super important for us. Thanks to 
 [cobra](https://github.com/spf13/cobra). It powers us to do a better job.
 
-## Jenkins API
+## Jenkins REST API
 
-API is another important part of this project. `jcli` manages your Jenkins by the HTTP API.
-There's no official documents for this. You can figure it by yourself, or just join our
-[gitter room](https://gitter.im/jenkinsci/jenkins-cli).
+API is another important part of this project. `jcli` manages Jenkins by the REST API.
+There is no full specification for this API at the moment, Jenkins core and plugins provide documentation independently.
+You can figure it by yourself, or just join our
+[gitter room](https://gitter.im/jenkinsci/jenkins-cli) to ask about specific APIs if needed.
+
+Useful links:
+
+* [Jenkins Remote Access API](https://wiki.jenkins.io/display/JENKINS/Remote+access+API)
+* [Jenkins REST API overview](https://www.youtube.com/watch?v=D93t1jElt4Q) by [Cliffano Subagio](https://github.com/cliffano)
+* 
 
 ## Testing
 
-We use a BDD Testing Framework to test our project. Please make sure you're familar
+We use a BDD Testing Framework to test our project. Please make sure you're familiar
 with [ginkgo](https://github.com/onsi/ginkgo) before you get start to contribute.
 
 ## Pull Requests
 
-Before you get start, please fork this project into your GitHub account firstly. Then
+Before you get started, please fork this project into your GitHub account. Then
 create a git branch base on what you want to improve. Please consider **never** using
-the master branch as your develope branch. And the behaviour of the git **force push** is not
-encourage.
+the master branch as your development branch. And the behaviour of the git **force push** is not
+encouraged when submitting pull requests.
 
-Please **don't** create another Pull Request if you messed up your git commit records.
+Please **do not** create another Pull Request if you messed up your git commit records.
 
-In order to generate a nice [release notes](https://github.com/jenkins-zh/jenkins-cli/releases),
+In order to generate nice [release notes](https://github.com/jenkins-zh/jenkins-cli/releases),
 please consider writing a proper Pull Request title.
 [release-draft](https://github.com/toolmantim/release-drafter) will generate the notes base your title.
 
-## Qulity
+## Quality
 
-Qulity is the heart of a project. So please make sure your Pull Request could pass the
-[Sonar Qulity Gate](https://sonarcloud.io/dashboard?id=jenkins-zh_jenkins-cli).
+Quality is the heart of a project. So please make sure your Pull Request could pass the
+[Sonar Quality Gate](https://sonarcloud.io/dashboard?id=jenkins-zh_jenkins-cli).
 
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