Add pyright language server support for python-mode

* eglot.el (eglot-server-programs): Add pyright support for
python-mode.
* README.md: Document the above change.

Copyright-paperwork-exempt: Yes

README.md

@@ -40,7 +40,7 @@ find-library` can help you tell if that happened.
 
 * Javascript's [TS & JS Language Server ][typescript-language-server]
 * Rust's [rls][rls]
-* Python's [pylsp][pylsp] or [pyls][pyls] 
+* Python's [pylsp][pylsp], [pyls][pyls] or [pyright][pyright]
 * Ruby's [solargraph][solargraph]
 * Java's [Eclipse JDT Language Server][eclipse-jdt]
 * Bash's [bash-language-server][bash-language-server]
@@ -547,6 +547,7 @@ Under the hood:
 [rls]: https://github.com/rust-lang-nursery/rls
 [pyls]: https://github.com/palantir/python-language-server
 [pylsp]: https://github.com/python-lsp/python-lsp-server
+[pyright]: https://github.com/microsoft/pyright
 [gnuelpa]: https://elpa.gnu.org/packages/eglot.html
 [melpa]: https://melpa.org/#/eglot
 [typescript-language-server]: https://github.com/theia-ide/typescript-language-server

eglot.el

@@ -141,7 +141,8 @@ chosen (interactively or automatically)."
 
 (defvar eglot-server-programs `((rust-mode . (eglot-rls "rls"))
                                 (python-mode
-                                 . ,(eglot-alternatives '("pylsp" "pyls")))
+                                 . ,(eglot-alternatives
+                                     '("pylsp" "pyls" ("pyright-langserver" "--stdio"))))
                                 ((js-mode typescript-mode)
                                  . ("typescript-language-server" "--stdio"))
                                 (sh-mode . ("bash-language-server" "start"))