Change default values for base config macros

Example $(hostname) is now equal to $(primary_domain).

$(local_domains) now contains only $(primary_domain).

tls directive contains values that represent certbot
store structure, allowing easier configuration by symlinking
/etc/maddy/certs to /etc/letscrypt/live.

README.md

@@ -99,7 +99,7 @@ $HOME/go/bin).
 ## Quick start
 
 *Note*: explaination below is short and assumes that you already have
-base ideas about how email works. If you are not sure, Project Wiki 
+basic ideas about how email works. If you are not sure, Project Wiki 
 contains a [more detailed tutorial](https://github.com/foxcpp/maddy/wiki/Setting-up-a-mail-server-with-maddy).
 
 1. Install maddy and maddyctl (see above)
@@ -109,14 +109,12 @@ contains a [more detailed tutorial](https://github.com/foxcpp/maddy/wiki/Setting
    see `maddy -help`.
 4. Open maddy.conf with ~~vim~~your favorite editor and change 
    the following:
-- `tls cert_file key_file` 
+- `tls ...` 
   Change to paths to TLS certificate and key.
-- `hostname`
+- `$(hostname)`
   Server identifier. Put your domain here if you have only one server.
 - `$(primary_domain)`
   Put the "main" domain you are handling messages for here.
-- `$(local_domains)`
-  If you have additional domains you want to accept mail for - put them here.
 5. Run the executable.
 6. On first start-up server will generate a RSA-2048 keypair for DKIM and tell
    you where file with DNS record text is placed. You need to add it to your

maddy.conf

@@ -1,26 +1,28 @@
-# Location of TLS certificate and private key. Global directive is used for all
-# endpoints.
-tls cert_file_path pkey_file
-
 # hostname is the identifier of this mail server.
 # It is recommended to set it to the domain that resolves to the IP of this
 # server.
-hostname mx1.example.org
+$(hostname) = example.org
 
 # Primary domain is used as a sender of autogenerated messages and
-# ADMD for DKIM signatures. You might want to change later when
-# managing multiple domains.
+# ADMD for DKIM signatures.
+# For simple configurations, it is usually equal to $(hostname).
 $(primary_domain) = example.org
 
 # All domains we want to receive messages for.
-# Just remove 'example.com' here if you handle only $(primary_domain).
-$(local_domains) = $(primary_domain) example.com
+$(local_domains) = $(primary_domain)
+
+# Location of TLS certificate and private key. Global directive is used for all
+# endpoints.
+tls /etc/maddy/certs/$(hostname)/fullchain.pem \
+    /etc/maddy/certs/$(hostname)/privkey.pem
 
 # -------------
 # Below are all remaining details you probably don't have to care
 # about if you just want a working mail server.
 # -------------
 
+hostname $(hostname)
+
 # Domain that will be used in From field in auto-generated messages.
 # (notably, notifications about failed deliveries)
 autogenerated_msg_domain $(primary_domain)