Add README

README.md

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+# hive_mirror
+
+One way sync for hive databases.
+
+This package is in development. API might change.
+
+## Usage
+
+```dart
+// Hive setup has to be done using the HiveMirror api.
+HiveMirror.init('myHivePath');
+HiveMirror.registerAdapter(PersonAdapter());
+
+final source = FileDescriptor.file(
+  File('myFilePath'),
+  decode: (line) {
+    final tupple = line.split(':');
+    return Person()
+      ..name = tupple[0]
+      ..age = tupple[1];
+  },
+  decodeKey: (line) {
+    final tupple = line.split(':');
+    return tupple[0];
+  },
+);
+
+// Box is synced with the data source
+final box = await Hive.openMirrorBox<Person>('myBox', mirrorSource: source);
+```
+
+## Supported backends
+
+HiveMirror currently supports files and git patches data sources.
+
+### Text file
+
+Both local and remote files are supported as mirror data sources.
+Each line of the file must describe a box entry which is decoded and put in the box during the mirror operation.
+A file is processed only if it has changed since the last mirror operation.
+
+```dart
+final source = FileDescriptor.file(
+  File('myFilePath'),
+  decode: (line) {
+    final tupple = line.split(':');
+    return Person()
+      ..name = tupple[0]
+      ..age = tupple[1];
+  },
+  decodeKey: (line) {
+    final tupple = line.split(':');
+    return tupple[0];
+  },
+);
+```
+
+### Git patch
+
+HiveMirror relies on git patches to support incremental sync.
+A git patch is formatted using the commit from the last mirror operation.
+Each diff line is then decoded and either put or deleted from the box.
+
+Github compare view is used as the patch provider.
+
+```dart
+final source = GitPatch.githubCompareView('myGithubUserName', 'myRepoName',
+  initialBaseRevision: 'initialRevision',
+  compareRevision: 'master',
+  filter: (filePath) => filePath == 'myFileToSync',
+  decode: (filePath, line) {
+    final tupple = line.split(':');
+    return Person()
+      ..name = tupple[0]
+      ..age = tupple[1];
+  },
+  decodeKey: (filePath, line) {
+    final tupple = line.split(':');
+    return tupple[0];
+  },
+);
+```
+
+## Limitations
+
+HiveMirror operates inside an isolate. So it will not work in flutter web.