Fill description of this repo

README.md

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 # intro-to-github
 This is a demo repository to practice using GitHub.
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+It has two files in the *Code* tab:
+- *README.md* is the description of this repo (you are currently reading it)
+- *.gitignore* is a file that specifies which filse and directories must be ignored by Git
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+You cannot make changes in these files directly because you are not collaborator.
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+The *Issues* tab is used to discuss ideas, enchacements, bugs, questions, and so on. Each *Issue* has a status.
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+The *Pull requests* tab contains proposals to make some changes in the files located in the repository. Repo's owners may review a request and put your changes if they look good.
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+You can create an *Issue* or make a *Pull request* to contribute in the project.