Add Flycheck plugin

plugins/flycheck/flycheck-proselint.el

@@ -0,0 +1,16 @@
+; To install flycheck from MELPA, evaluate:
+;
+; (add-hook 'markdown-mode-hook #'flycheck-mode)
+; (add-hook 'text-mode-hook #'flycheck-mode)
+
+(flycheck-define-checker proselint
+  "A linter for prose."
+  :command ("proselint" source-inplace)
+  :error-patterns
+  ((warning line-start (file-name) ":" line ":" column ": "
+            (id (one-or-more (not (any " "))))
+            (message (one-or-more not-newline)
+                     (zero-or-more "\n" (any " ") (one-or-more not-newline)))
+            line-end))
+  :modes (text-mode markdown-mode gfm-mode))
+(add-to-list 'flycheck-checkers 'proselint)