set the default keystore to the same as the default in fdroid init

This should keep things simple and consistent.

examples/config.py

@@ -60,7 +60,7 @@ repo_keyalias = None
 
 #The keystore to use for release keys when building. This needs to be
 #somewhere safe and secure, and backed up!
-keystore = "/home/me/somewhere/my.keystore"
+#keystore = "/home/me/.local/share/fdroidserver/keystore.jks"
 
 # The password for the keystore (at least 6 characters).  If this password is
 # different than the keypass below, it can be OK to store the password in this

fdroidserver/common.py

@@ -66,6 +66,8 @@ def read_config(opts, config_file='config.py'):
         'stats_to_carbon': False,
         'repo_maxage': 0,
         'build_server_always': False,
+        'keystore': os.path.join(os.getenv('HOME'),
+                                 '.local', 'share', 'fdroidserver', 'keystore.jks'),
         'char_limits': {
             'Summary' : 50,
             'Description' : 1500