Move files to '.github' directory (#15370)

.github/ISSUE_TEMPLATE.md

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+- [ ] I tried using the `@types/xxxx` package and had problems.
+- [ ] I tried using the latest stable version of tsc. https://www.npmjs.com/package/typescript
+- [ ] I have a question that is inappropriate for [StackOverflow](https://stackoverflow.com/).  (Please ask any appropriate questions there).
+- [ ] [Mention](https://github.com/blog/821-mention-somebody-they-re-notified) the authors (see `Definitions by:` in `index.d.ts`) so they can respond.
+  - Authors: @....

.github/PULL_REQUEST_TEMPLATE.md

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+Please fill in this template.
+
+- [ ] Make your PR against the `master` branch.
+- [ ] Use a meaningful title for the pull request. Include the name of the package modified.
+- [ ] Test the change in your own code. (Compile and run.)
+- [ ] Follow the advice from the [readme](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/README.md#make-a-pull-request).
+- [ ] Avoid [common mistakes](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/README.md#common-mistakes).
+- [ ] Run `tsc` without errors.
+- [ ] Run `npm run lint package-name` if a `tslint.json` is present.
+
+Select one of these and delete the others:
+
+If adding a new definition:
+- [ ] The package does not provide its own types, and you can not add them.
+- [ ] If this is for an NPM package, match the name. If not, do not conflict with the name of an NPM package.
+- [ ] Create it with `npm run new-package package-name`, not by basing it on an existing project.
+- [ ] `tslint.json` should be present, and `tsconfig.json` should have `noImplicitAny`, `noImplicitThis`, and `strictNullChecks` set to `true`.
+
+If changing an existing definition:
+- [ ] Provide a URL to documentation or source code which provides context for the suggested changes: <<url here>>
+- [ ] Increase the version number in the header if appropriate.
+- [ ] If you are making substantial changes, consider adding a `tslint.json` containing `{ "extends": "../tslint.json" }`.
+
+If removing a declaration:
+- [ ] If a package was never on DefinitelyTyped, you don't need to do anything. (If you wrote a package and provided types, you don't need to register it with us.)
+- [ ] Delete the package's directory.
+- [ ] Add it to `notNeededPackages.json`.