add nnstreamer-example sources for practice

[JawThrow]

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[Template] PR Description

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Summarize changes in around 50 characters or less

More detailed explanatory text, if necessary. Wrap it to about 72
characters or so. In some contexts, the first line is treated as the
subject of the commit and the rest of the text as the body. The
blank line separating the summary from the body is critical;
various tools like `log`, `shortlog` and `rebase` can get confused 
if you run the two together.

Further paragraphs come after blank lines.

**Changes proposed in this PR:**
- Bullet points are okay, too
- Typically a hyphen or asterisk is used for the bullet, preceded
  by a single space, with blank lines in between, but conventions vary here.

Resolves: #123
See also: #456, #789

**Self evaluation:**
1. Build test: [ ]Passed [ ]Failed [*]Skipped
2. Run test: [ ]Passed [ ]Failed [* ]Skipped

**How to evaluate:**
1. Describe how to evaluate in order to be reproduced by reviewer(s).

Add signed-off message automatically by running **$git commit -s ...** command.

$ git push origin <your_branch_name>

[taos-ci]

:memo: Version: 1.20190225. Thank you for submitting PR #221. Your PR must pass all verificiation processes of cibot before starting a review process from reviewers. If you are new member to join this project, please read manuals in documentation folder and wiki page. In order to monitor a progress status of your PR in more detail, visit http://nnsuite.mooo.com/.

[taos-ci]

:octocat: cibot: @JawThrow, **** does not include doxygen tags such as . You must include the doxygen tags in the source code at least.

[taos-ci]

:octocat: cibot: @JawThrow, You wrote code with incorrect doxygen statements. Please check a doxygen rule at http://github.com/nnsuite/TAOS-CI/blob/master/ci/doc/doxygen-documentation.md

[taos-ci]

:octocat: cibot: @JawThrow, There is a newline issue. The final line of a text file should have newline character. Please resubmit your PR after fixing end of line in .vscode/settings.json.

[taos-ci]

To contributor, We have used 'Signed-off-by:' notation by default to handle the license issues, that result from contributors. Note that 'Is there a Signed-off-by line?' is important because lawyers tell us we must have to it to cleanly maintain the open-source license issues even though it has nothing to do with the code itself.

[taos-ci]

:octocat: cibot: @JawThrow, One of the format checkers is failed. If you want to get a hint to fix this issue, please go to https://github.com/nnstreamer/nnstreamer-example/wiki/.