Update mg_base64_decode.md

docs/c-api/util.h/mg_base64_decode.md

@@ -6,11 +6,11 @@ signature: |
   int mg_base64_decode(const unsigned char *s, int len, char *dst);
 ---
 
-Decode base64-encoded string `s`, `len` into the destination `dst`.
-Destination has to have enough space to hold decoded buffer.
-Decoding stops either when all string has been decoded, or invalid
+Decodes base64-encoded string `s`, `len` into the destination `dst`.
+The destination has to have enough space to hold the decoded buffer.
+Decoding stops either when all strings have been decoded or invalid an
 character appeared.
 Destination is '\0'-terminated.
-Return number of decoded characters. On success, that should be equal to
+Returns the number of decoded characters. On success, that should be equal to
 `len`. On error (invalid character) the return value is smaller then `len`.