[BUGFIX] Grammar fix (added period to README)

[fredster33]

Description

This is just a small grammar fix to the README.

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

Changes

• Grammar fix to README (I haven't run tests on the rest of the repo, but assume that they will pass as I haven't changed anything except for the README)

Comments

None!

[mxnet-bot]

Hey @fredster33 , Thanks for submitting the PR
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[fredster33]

@mxnet-bot run ci [all]

[mxnet-bot]

Jenkins CI successfully triggered : [centos-cpu, unix-cpu, website, clang, unix-gpu, edge, sanity, miscellaneous, centos-gpu, windows-gpu, windows-cpu]