Record why DISABLE_VERIFY_CERTIFICATE never worked

The daemon reads the key with seafile_session_config_get_bool, which is a
case sensitive g_strcmp0(value, "true"), so the capitalised True stored by
released images up to 0.0.13 was read as false and verification stayed on for
anyone who asked to disable it. The default was never affected, since any
value other than "true" is false.

Rendering booleans in lower case fixed this; this only writes down what the
change actually repaired, for anyone who reported the flag as broken.

README.md

@@ -47,7 +47,10 @@ volumes:
  confirmation before being deleted simultaneously. Default value is _500_.
  - `DISABLE_VERIFY_CERTIFICATE` - set to _true_ to disable server's certificate
  verification. Default value is _false_. Booleans accept _true_/_false_,
- _1_/_0_, _yes_/_no_ and _on_/_off_, in any case.
+ _1_/_0_, _yes_/_no_ and _on_/_off_, in any case. Note that this setting had no
+ effect in released images up to and including 0.0.13: the value reached the
+ Seafile daemon capitalised, which it does not recognise, so verification
+ stayed on even when the variable was set. The default was never affected.
  - `UPLOAD_LIMIT` / `DOWNLOAD_LIMIT` -  upload/download speed limit in B/s
  (bytes per second). Default values are _0_ (unlimited).