[lit] Deduplicate README and longdescription, and update it

[mgorny]

Summary

Since long_description is effectively the README that's displayed
on pypi project page, combine it with the existing README file and read
the file in setup.py. This is a common practice among Python
projects, to the point of declarative-style setuptools configurations
providing a shorthand for it.

While at it, update the outdated information about LLVM Bugzilla for use
of GitHub issues.

[mgorny]

llvm/utils/lit/README.rst

27

I've left the verbose URLs since this is how long_description previously did it. If you prefer, I can change them to proper ReST links.

[serge-sans-paille]

I'm fine with the change. Thanks!

llvm/utils/lit/README.rst

41

optional: mention the link https://github.com/llvm/llvm-project/labels/tools%3Allvm-lit

[MaskRay]

llvm/utils/lit/README.rst

50

[mgorny]

Thanks!

llvm/utils/lit/README.rst

 ===============================
  lit - A Software Testing Tool
 ===============================
 
-lit is a portable tool for executing LLVM and Clang style test suites,
-summarizing their results, and providing indication of failures. lit is designed
-to be a lightweight testing tool with as simple a user interface as possible.
+About
+=====
+
+*lit* is a portable tool for executing LLVM and Clang style test suites,
+summarizing their results, and providing indication of failures. *lit* is
+designed to be a lightweight testing tool with as simple a user interface as
+possible.
+
+
+Features
+========
+
+ * Portable!
+ * Flexible test discovery.
+ * Parallel test execution.
+ * Support for multiple test formats and test suite designs.
+
+
+Documentation
+=============
+
+The official *lit* documentation is in the man page, available online at the LLVM
+Command Guide: http://llvm.org/cmds/lit.html.
+
+
+Source
+======
+
+The *lit* source is available as part of LLVM, in the LLVM source repository:
+https://github.com/llvm/llvm-project/tree/main/llvm/utils/lit
+
 
-=====================
- Contributing to lit
-=====================
+===================
 
-Please browse the Test Suite > lit category in LLVM's Bugzilla for ideas on
-what to work on.
+Please browse the issues labeled *tools:llvm-lit* in LLVM's issue tracker for
+ideas on what to work on.
 
 Before submitting patches, run the test suite to ensure nothing has regressed:
 
     # From within your LLVM source directory.
     utils/lit/lit.py \
         --path /path/to/your/llvm/build/bin \
         utils/lit/tests
 
-Note that lit's tests depend on 'not' and 'FileCheck', LLVM utilities.
+Note that lit's tests depend on *not* and *FileCheck*, LLVM utilities.
 You will need to have built LLVM tools in order to run lit's test suite
 successfully.
 
 You'll also want to confirm that lit continues to work when testing LLVM.
 Follow the instructions in http://llvm.org/docs/TestingGuide.html to run the
 regression test suite:
 
     make check-llvm

llvm/utils/lit/setup.py

 import lit
 import os
 
 from setuptools import setup, find_packages
 
 # setuptools expects to be invoked from within the directory of setup.py, but it
 # is nice to allow:
 #   python path/to/setup.py install
 # to work (for scripts, etc.)
 os.chdir(os.path.dirname(os.path.abspath(__file__)))
 
+with open("README.rst", "r", encoding="utf-8") as f:
+    long_description = f.read()
+
 setup(
     name = "lit",
     version = lit.__version__,
 
     author = lit.__author__,
     author_email = lit.__email__,
     url = 'http://llvm.org',
     license = 'Apache-2.0 with LLVM exception',
     license_files = ['LICENSE.TXT'],
 
     description = "A Software Testing Tool",
     keywords = 'test C++ automatic discovery',
-    long_description = """\
-*lit*
-+++++
-
-About
-=====
-
-*lit* is a portable tool for executing LLVM and Clang style test suites,
-summarizing their results, and providing indication of failures. *lit* is
-designed to be a lightweight testing tool with as simple a user interface as
-possible.
-
-
-Features
-========
-
- * Portable!
- * Flexible test discovery.
- * Parallel test execution.
- * Support for multiple test formats and test suite designs.
-
-
-Documentation
-=============
-
-The official *lit* documentation is in the man page, available online at the LLVM
-Command Guide: http://llvm.org/cmds/lit.html.
-
-
-Source
-======
-
-The *lit* source is available as part of LLVM, in the LLVM source repository:
-https://github.com/llvm/llvm-project/tree/main/llvm/utils/lit
-""",
+    long_description = long_description,
 
     classifiers=[
         'Development Status :: 3 - Alpha',
         'Environment :: Console',
         'Intended Audience :: Developers',
         'License :: OSI Approved :: Apache Software License',
         'Natural Language :: English',
         'Operating System :: OS Independent',