Update README.md to document the "codeium_render" option (Exafunction#339)

* Update README.md

Author: ilan-schemoul

README.md

@@ -134,6 +134,12 @@ completions:
 let g:codeium_manual = v:true
 ```
 
+To disable automatic text rendering of suggestions (the gray text that appears for a suggestion):
+
+```vim
+let g:codeium_render = v:false
+```
+
 ### Show Codeium status in statusline
 
 Codeium status can be generated by calling the `codeium#GetStatusString()` function. In