Add implementations declaration

Author: devanych

composer.json

@@ -1,6 +1,6 @@
 {
     "name": "httpsoft/http-response",
-    "description": "PSR-7 implementation for Response",
+    "description": "PSR-7 Response implementations",
     "keywords": ["php", "http", "http-response", "responses", "psr-7", "http-message"],
     "homepage": "https://httpsoft.org/",
     "type": "library",
@@ -27,6 +27,9 @@
         "squizlabs/php_codesniffer": "^3.5",
         "vimeo/psalm": "^3.14"
     },
+    "provide": {
+        "psr/http-message-implementation": "1.0"
+    },
     "autoload": {
         "psr-4": {
             "HttpSoft\\Response\\": "src/"