doc: add mode to uast documentation

Signed-off-by: Javi Fontan <[email protected]>

Author: jfontan

docs/using-gitbase/functions.md

@@ -9,7 +9,7 @@ To make some common tasks easier for the user, there are some functions to inter
 |is_remote(reference_name)bool| check if the given reference name is from a remote one                               |
 |is_tag(reference_name)bool| check if the given reference name is a tag                                              |
 |language(path, [blob])text| gets the language of a file given its path and the optional content of the file         |
-|uast(blob, [lang, [xpath]])json_blob| returns an array of UAST nodes as blobs                                       |
+|uast(blob, [lang, [xpath, [mode]]])json_blob| returns an array of UAST nodes as blobs, you can specify a mode (annotated, semantic or native) |
 |uast_xpath(json_blob, xpath)| performs an XPath query over the given UAST nodes                                     |
 
 ## Standard functions