Add go-langserver ()

Copyright-paperwork-exempt: yes

* README.md (Installation and usage): Add go-langserver.
* eglot.el (eglot-server-programs): Add go-langserver.

GitHub-reference: joaotavora/eglot#74

lisp/progmodes/eglot.el

@@ -91,7 +91,8 @@
                                 (php-mode . ("php" "vendor/felixfbecker/\
 language-server/bin/php-language-server.php"))
                                 (haskell-mode . ("hie-wrapper"))
-                                (kotlin-mode . ("kotlin-language-server")))
+                                (kotlin-mode . ("kotlin-language-server"))
+                                (go-mode . ("go-langserver" "-mode=stdio" "-gocodecompletion")))
   "How the command `eglot' guesses the server to start.
 An association list of (MAJOR-MODE . CONTACT) pairs.  MAJOR-MODE
 is a mode symbol, or a list of mode symbols.  The associated