Documentation: minor RST syntax fixes

- Fix bad link syntax
- Fix compilation warning

doc/030_preparing_a_new_repo.rst

@@ -369,8 +369,7 @@ key file and the project ID as follows:
     $ export GOOGLE_PROJECT_ID=123123123123
     $ export GOOGLE_APPLICATION_CREDENTIALS=$HOME/.config/gs-secret-restic-key.json
 
-Restic uses  Google's client library to generate [default authentication
-material](https://developers.google.com/identity/protocols/application-default-credentials),
+Restic uses  Google's client library to generate `default authentication material`_,
 which means if you're running in Google Container Engine or are otherwise
 located on an instance with default service accounts then these should work out
 the box.
@@ -393,6 +392,7 @@ established.
 
 .. _service account: https://cloud.google.com/storage/docs/authentication#service_accounts
 .. _create a service account key: https://cloud.google.com/storage/docs/authentication#generating-a-private-key
+.. _default authentication material: https://developers.google.com/identity/protocols/application-default-credentials
 
 Other Services via rclone
 *************************

doc/100_references.rst

@@ -625,9 +625,9 @@ are deleted, the particular snapshot vanished and all snapshots
 depending on data that has been added in the snapshot cannot be restored
 completely. Restic is not designed to detect this attack.
 
-******
+************
 Local Cache
-******
+***********
 
 In order to speed up certain operations, restic manages a local cache of data.
 This document describes the data structures for the local cache with version 1.