add README.md

Author: gilteunchoi

README.md

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+<img src="./logo.png" width="125" height="125" align="right" />
+
+# rustpython-doc
+
+This `rustpython-doc` package contains all `__doc__` database in forms of `docs.inc.rs`. 
+
+## How to update `__doc__` in RustPython
+
+Adding a remake in front of `[pyclass]` of `[pyfunction]` will simply make the documentation to themselves, however, we do not manually add docs anymore.
+
+> But we don't manually add docs anymore. We have an auto-generated document db.
+> 
+> The db is generated by scripts/generate_docs.py and applied to each object and functions by rustpython-doc::Database (search for crate::doc::Database::shared() in source code)
+> 
+> *- Originally posted by @youknowone in [RustPython#4205 (comment)](https://github.com/RustPython/RustPython/pull/4205)*
+
+Therefore you must update `docs.in.rs`, if it is unnecessary to different from cpython's `__doc__`
+
+## How to update `docs.in.rs`
+
+To update  `__doc__` for newer python version:
+
+```
+$ python generate_docs.py {RustPython PATH} ./docs.inc.rs
+```
+This will iterate all stdlib modules to inspect their `__doc__`, updating your local `docs.in.rs` file. Since RustPython is only able to access the database in this online package, the changes must be merged into this branch.
+
+After that, update cargo:
+```
+$ cargo update
+```
+## Why the `__doc__` is not changed?
+
+### Check if it is related to the unclosed issue
+There is still some issue with `generate_docs.py`
+- https://github.com/RustPython/RustPython/issues/3973
+
+
+
+### Check if the old remark documentation are not removed yet
+
+RustPython prioritizes the user define documentation first. Check if old remarks remaining in the source code, and remove them.