fix: unhappy readme formatting

twine check complains that the readme.rst is invalid. Looking at the
current pypi I see this warning is valid and nothing is rendered on
the existing 2.0.0 release. Convert rst to markdown.

README.md

@@ -0,0 +1,121 @@
+# jsondiff
+
+Diff JSON and JSON-like structures in Python.
+
+## Installation
+
+``pip install jsondiff``
+
+## Quickstart
+
+```python
+>>> import jsondiff as jd
+>>> from jsondiff import diff
+
+>>> diff({'a': 1, 'b': 2}, {'b': 3, 'c': 4})
+{'c': 4, 'b': 3, delete: ['a']}
+
+>>> diff(['a', 'b', 'c'], ['a', 'b', 'c', 'd'])
+{insert: [(3, 'd')]}
+
+>>> diff(['a', 'b', 'c'], ['a', 'c'])
+{delete: [1]}
+
+# Typical diff looks like what you'd expect...
+>>> diff({'a': [0, {'b': 4}, 1]}, {'a': [0, {'b': 5}, 1]})
+{'a': {1: {'b': 5}}}
+
+# ...but similarity is taken into account
+>>> diff({'a': [0, {'b': 4}, 1]}, {'a': [0, {'c': 5}, 1]})
+{'a': {insert: [(1, {'c': 5})], delete: [1]}}
+
+# Support for various diff syntaxes
+>>> diff({'a': 1, 'b': 2}, {'b': 3, 'c': 4}, syntax='explicit')
+{insert: {'c': 4}, update: {'b': 3}, delete: ['a']}
+
+>>> diff({'a': 1, 'b': 2}, {'b': 3, 'c': 4}, syntax='symmetric')
+{insert: {'c': 4}, 'b': [2, 3], delete: {'a': 1}}
+
+>>> diff({'list': [1, 2, 3], "poplist": [1, 2, 3]}, {'list': [1, 3]}, syntax="rightonly")
+{"list": [1, 3], delete: ["poplist"]}
+
+# Special handling of sets
+>>> diff({'a', 'b', 'c'}, {'a', 'c', 'd'})
+{discard: set(['b']), add: set(['d'])}
+
+# Load and dump JSON
+>>> print diff('["a", "b", "c"]', '["a", "c", "d"]', load=True, dump=True)
+{"$delete": [1], "$insert": [[2, "d"]]}
+
+# NOTE: Default keys in the result are objects, not strings!
+>>> d = diff({'a': 1, 'delete': 2}, {'b': 3, 'delete': 4})
+>>> d
+{'delete': 4, 'b': 3, delete: ['a']}
+>>> d[jd.delete]
+['a']
+>>> d['delete']
+4
+# Alternatively, you can use marshal=True to get back strings with a leading $
+>>> diff({'a': 1, 'delete': 2}, {'b': 3, 'delete': 4}, marshal=True)
+{'delete': 4, 'b': 3, '$delete': ['a']}
+```
+
+## Command Line Client
+
+Usage:
+```
+jdiff [-h] [-p] [-s {compact,symmetric,explicit}] [-i INDENT] [-f {json,yaml}] first second
+
+positional arguments:
+  first
+  second
+
+optional arguments:
+  -h, --help            show this help message and exit
+  -p, --patch
+  -s {compact,symmetric,explicit}, --syntax {compact,symmetric,explicit}
+                        Diff syntax controls how differences are rendered (default: compact)
+  -i INDENT, --indent INDENT
+                        Number of spaces to indent. None is compact, no indentation. (default: None)
+  -f {json,yaml}, --format {json,yaml}
+                        Specify file format for input and dump (default: json)
+```
+
+Examples:
+
+```bash
+$ jdiff a.json b.json -i 2
+
+$ jdiff a.json b.json -i 2 -s symmetric
+
+$ jdiff a.yaml b.yaml -f yaml -s symmetric
+```
+
+## Development
+
+Install development dependencies and test locally with
+
+```bash
+pip install -r requirements-dev.txt
+# ... do your work ... add tests ...
+pytest
+```
+
+## Installing From Source
+
+To install from source run
+
+```bash
+pip install .
+```
+
+This will install the library and cli for `jsondiff` as well as its runtime
+dependencies.
+
+
+## Testing before release
+
+```bash
+python -m build
+twine check dist/*
+```

pyproject.toml

@@ -6,7 +6,7 @@ build-backend = "setuptools.build_meta"
 name = "jsondiff"
 description = "Diff JSON and JSON-like structures in Python"
 dynamic = ["version", "dependencies", "optional-dependencies"]
-readme = "README.rst"
+readme = "README.md"
 license= {file = "LICENSE" }
 requires-python = ">=3.8"
 authors = [