Make it easier to get started adjusting PEP8

I added quick start guide how to adjust pep8 settings. This will make SublimeLinter-pep8 more friendly towards new users who might have hard time to find how the settings work through all Sublime Text and SublimeLinter settings layers.
Please change it to this:

```text
### Implementing per-project settings
Typically you will want to configure pep8 on a per-project basis to conform to the coding style for all files in that project. Usually you want to ignore certain pep8 warnings. First you need to find the pep8 error codes from the [pep8 documentation](http://pep8.readthedocs.org/en/latest/intro.html#error-codes). Then you need to configure the pep8 linter to ignore those warnings.

For example, let’s say your project requires python 2.7+, you want the maximum line length to be 512, and you want to ignore warnings about visual indents (pep8 errors E127 and E128):

* If you have not already created a project in Sublime Text, select `Project -> Save Project As...`.

* Select `Project -> Edit Project`.

* At the **top** level of the project’s JSON data, add the following:

        "SublimeLinter":
        {
            "@python": 2.7,
            "linters":
            {
                "pep8":
                {
                    "@disable": false,
                    "ignore": "E127,E128",
                    "max-line-length": 512
                }
            }
        }

* Save the file.

Any time you edit the project and change a linter’s settings, all open files that use that linter will be re-linted to reflect the new settings.
```