[imp] Update CONTRIBUTING.md. Closes joomla#4915

Followed the normal style of using the long form 'pull request' once with short form in brackets (PR) which enables PR to be used for the rest of the document. Grammar and small change for readability.

CONTRIBUTING.md

@@ -1,25 +1,26 @@
-Contributing to the Joomla! CMS
+Contributing to the Joomla! CMS™
 ===============
-All contributions are welcome to be submitted for review for inclusion in the Joomla! CMS, but before they will be accepted, we ask that you follow these simple steps:
+You are welcome to submit a contribution for review and possible inclusion in the Joomla! CMS but, before it will be accepted, we ask that you follow these simple steps:
 
-1) Open an issue on our [Issue Tracker](http://issues.joomla.org/) or here on GitHub. If you can provide a fix create a pull request instead, it will automatically create the issue for you.
+1) Open an issue on our [Issue Tracker](http://issues.joomla.org/) or here on GitHub. If you can, please provide a fix and create a pull request (PR) instead; this will automatically create an issue for you.
 
-2) Follow the [Joomla! Coding Standards](http://joomla.github.io/coding-standards)!
+2) Follow the [Joomla! Coding Standards](http://joomla.github.io/coding-standards).
 
-3) When filing an issue or opening a pull request, please include a clear title and description.  The title should be a short summary of an issue and if possible, should include a reference to an open issue.  For example, `Invalid Query in com_admin (Ref #1234)` would be sufficient.  All issues and pull requests should include a description with as much detail as possible, including what the issue is, (if a pull request) what the pull request is addressing as well as testing instructions, and environmental information (PHP version, database driver and version, and other data you would retrieve from your site's System Information view) in case the issue is specific to certain environments.  If additional information is needed, please be prepared to provide it as our community members review your submission.
+3) When filing an issue or opening a PR, please include a clear title and description.  The title should be a short summary of an issue and, if possible, should include a reference to an open issue.  For example, `Invalid Query in com_admin (Ref #1234)` would be sufficient.  All issues and PRs should include a description with as much detail as possible. 
+If it is a PR, include what the issue is, what the PR is addressing, testing instructions and environmental information (PHP version, database driver and version, and other data you can retrieve from your site's system information view) in case the issue is specific to certain environments.  If additional information is needed, please be prepared to provide it as our community members review your submission.
 
-4) Report security issues to the Joomla! Security Strike Team (JSST) at security@joomla.org or with the [JSST contact form](http://developer.joomla.org/contact-security-team.html), please do not use the public tracker for security issues.
+4) Report security issues to the Joomla! Security Strike Team (JSST) at security@joomla.org or use the [JSST contact form](http://developer.joomla.org/contact-security-team.html). Please do not use the public tracker for security issues.
 
 Please be patient as not all items will be tested immediately (remember, all bug testing for the Joomla! CMS is done by volunteers) and be receptive to feedback about your code.
 
 #### Branches
-Pull Requests should usually be made for the `staging` branch as this contains the most recent version of the code.
+PRs should usually be made to the `staging` branch as this contains the most recent version of the code.
 There are other branches available which serve specific purposes.
 
 | Branch | Purpose |
 | ------ | ------- |
 | staging | Current codebase. |
-| master | Each commit made to staging gets tested if it passes unit tests and codestyle rules and then merged into master. This is done automatically. |
+| master | Each commit made to staging gets tested if it passes unit tests and codestyle rules. It is then merged into master. This is done automatically. |
 | 2.5.x | Branch for the Joomla 2.5.x series. Currently in maintenance mode with EOL end of 2014. No new features are accepted here. |
 | 3.2.x | Branch for the Joomla 3.2.x series. Currently in security mode with EOL Oct 2014. Only security issues are fixed. |
 | 3.4-dev | Branch for the next minor Joomla version. New backward compatible features go into this branch. Commits to staging will be applied to this branch as well. |