[Doc] Update PULL_REQUEST_TEMPLATE.md: a reword suggestion

[Sunt-ing]

This is a basic grammatical modification suggestion, which will not break any existing build.

Proposed changes

A reword suggestion. Change
from "I have create an issue on (Fix #ISSUE), and have described the bug/feature there in detail"
to "I have created an issue on (Fix #ISSUE) and described the bug/feature there in detail"

Targets:

1. Eliminate a basic grammar error.
2. Eliminate word redundancy, because redundancy makes the statement a little harder to understand. After changed, the statement gets a little more elegant.

Types of changes

• [] Bugfix (non-breaking change which fixes an issue)
• [] New feature (non-breaking change which adds functionality)
• [] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)
• [] Code refactor (Modify the code structure, format the code, etc...)

Checklist

The PR is very clear, and thus I think no issue is needed.
It's a simple reword suggestion, which will not break our project.

Further comments

It's very simple, and thus I don't think any additional comment is needed.

[yangzhg]

LGTM