add: CONTRIBUTING guide (#102)

1. It's a guideline to let people know how to contribute

CONTRIBUTING.md

@@ -0,0 +1,130 @@
+# Contributing to DeepLearningZeroToAll
+
+## Precheck steps
+
+* Before starting to work on something, **please leave an issue first.** Because
+  * It helps to let people know what you are working on
+  * A problem might have nothing to do with this repo
+  * It could be our intention to keep the code in that way (for [KISS](https://en.wikipedia.org/wiki/KISS_principle))
+* You should know how to use git
+  * If not, please google "how to use git." and read through them before you do anything. It's a mandatory skill to survive as a developer
+  * Try [git tutorial](https://try.github.io/levels/1/challenges/1)
+
+## Contribution guidelines
+
+This document will guide you through the contribution process.
+
+### Step 1: Fork
+
+Fork the project [on GitHub](https://github.com/hunkim/DeepLearningZeroToAll.git) by pressing the "fork" button.
+This step will copy this repository to your account so that you can start working on.
+
+### Step 2: Download to a local computer
+
+
+```bash
+$ git clone https://github.com/`YOUR_GITHUB_NAME`/DeepLearningZeroToAll.git
+$ cd DeepLearningZeroToAll
+```
+### Step 3: Setup an upstream
+
+It's always a good idea to set up a link to this repo so that you can pull easily if there were changes
+
+```bash
+$ git remote add upstream https://github.com/hunkim/DeepLearningZeroToAll.git
+```
+
+If there were updates in this repository, you can now keep your local copy and your repository updated
+
+```bash
+$ git pull upstream master && git push origin master
+```
+
+### Step 4: Make a branch
+
+You don't want to directly modify the master branch because the master branch keeps changing by merging PRs, etc.
+
+Also remember to give a meaningful name!
+
+Example: 
+```bash
+$ git checkout -b hotfix/lab10 -t origin/master
+```
+
+After making a new branch, feel free to modify the codes now!
+
+**Note: don't get tempted to fix other things that are not related to your issue.**
+Your commit should be in logical blocks! If it's a different problem, you have to create a separate issue.
+
+
+### Step 5: Commit
+
+If you have not set up, please set up your email/username 
+```bash
+$ git config --global user.name "Sung Kim"
+$ git config --global user.email "[email protected]"
+```
+
+then commit:
+```bash
+$ git add my/changed/files
+$ git commit
+```
+
+Notes
+* Write a clear commit message!
+* Example:
+```text
+Short (50 chars or less) summary of changes
+
+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 an email and the rest of the text as the body.  The blank
+line separating the summary from the body is critical (unless you omit
+the body entirely); tools like rebase can get confused if you run the
+two together.
+
+Further paragraphs come after blank lines.
+
+  - 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
+```
+
+### Step 6: (Optional) Rebase your branch
+
+If your fix is taking longer than usual, it's likely that your repo is outdated.  
+Sync your repo to the latest:
+```bash
+$ git fetch upstream
+$ git rebase upstream/master
+```
+
+### Step 7: Push
+
+Before pushing to YOUR REPO, make sure you run `autopep8`!
+
+Please follow PEP8 styles.  The only exception is `E501`(max-line-char limit)  
+**Remember: Readability > everything**
+
+Example:
+
+```bash
+$ autopep8 . -r -i --ignore E501
+$ git push -u origin hotfix/lab10
+```
+
+
+### Step 8: Creating the PR
+Now, if you open a browser and open this repo.  
+You will see the big green button saying "compare & pull request."
+
+* Please ensure you write a good title.
+* Don't just write filenames you modified.
+* **Explain what you did and why you did.**
+* Add a relevant issue number as well.
+
+
+Congratulations ! Your PR will be reviewed by collaborators.  
+Please check your PR pass the CI test as well.