feat: 초기 프로젝트 설정 및 룰.md 파일 추가

api.hyungi.net/node_modules/js-git/doc/mixins/mem-db.md

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+# mem-db mixin
+
+This mixin implements object store (normal and raw) and stores the data in memory.
+
+```js
+var memDb = require('js-git/mixins/mem-db');
+var repo = {};
+memDb(repo);
+repo.saveAs("blob", "Hello World", function (err, hash) {
+  if (err) throw err;
+  console.log("Blob saved with hash " + hash);
+});
+```
+
+This attaches the following interfaces onto the repo object passed in:
+
+ - `saveAs(type, body) => hash`
+ - `loadAs(type, hash) => body`
+ - `loadRaw(hash) => raw-binary`
+ - `saveRaw(hash, raw-binary) =>`
+
+All these functions are async and accept either a callback last or return a continuable.
+
+```js
+// Example using continuable interface from gen-run generator body.
+var commit = yield repo.loadAs("commit", commitHash);
+```