Chore: Improve README for custom handler (#51)

Author: chrishrb

README.md

@@ -59,7 +59,17 @@ require("lazy").setup({
             end
           end,
         },
-      },
+        rust = { -- custom handler to open rust's cargo packages
+          filetype = { "toml" }, -- you can also set the required filetype for this handler
+          filename = "Cargo.toml", -- or the necessary filename
+          handle = function(mode, line, _)
+            local crate = require("gx.helper").find(line, mode, "(%w+)%s-=%s")
+
+            if crate then
+              return "https://crates.io/crates/" .. crate
+            end
+          end,
+        },
       },
       handler_options = {
         search_engine = "google", -- you can select between google, bing, duckduckgo, and ecosia