describe how to report bugs in contribution guide and add missing Jump(row, col) to readme

CONTRIBUTING.md

@@ -1,3 +1,21 @@
+## Reporting an issue
+
+For reporting a bug, please make sure your report includes the following points.
+
+- How to reproduce it
+  - What text the textarea contained as pre-condition
+  - What operations you did
+  - What was the expected behavior
+  - What was the actual behavior
+- Environment
+  - Your terminal
+  - Rust version
+  - `tui` crate version
+
+An example of bug report: https://github.com/rhysd/tui-textarea/issues/1
+
+## Submitting a pull request
+
 Please ensure that all tests and linter checks passed on your branch before creating a PR which modifies some source files.
 
 To run tests: