Exclude README.rst from package archives

README.rst is a symlink to docs/guide.txt, which is the canonical
users guide.

Packages containing symlinks appear to cause problems on Windows so
exclude it from composer archive creation.

I think this won't prevent README content from being displayed on
packagist.org because that site apparently fetches READMEs directly from
GitHub, if it does cause problems, we can also add the "readme"
property: https://getcomposer.org/doc/04-schema.md#readme

Author: jparise

composer.json

@@ -11,6 +11,9 @@
         "php": ">=7.4",
         "pear/pear_exception": "1.0.1 || 1.0.2"
     },
+    "archive": {
+        "exclude": ["/README.rst"]
+    },
     "autoload": {
         "psr-0": {
             "Log": "./"