Merge pull request #1660 from barnumbirr/complete-default-config

conf: document the config keys missing from aptly.conf and the man page

system/t02_config/CreateConfigTest_gold

@@ -32,6 +32,17 @@ database_open_attempts: -1
 architectures:
 #    - amd64
 
+# Hash algorithms to write Acquire-By-Hash entries for, when a publish
+# has Acquire-By-Hash enabled. Each algorithm costs a full set of index
+# copies on every publish, which is felt most on S3-like storage where
+# every write is a round trip. An empty list defaults to all four.
+# Modern apt uses SHA256; MD5Sum and SHA1 are deprecated.
+acquire_by_hash_algorithms:
+    - MD5Sum
+    - SHA1
+    - SHA256
+    - SHA512
+
 # OBSOLETE
 # in aptly up to version 1.0.0, package files were stored in internal package pool
 # with MD5-dervied path, since 1.1.0 package pool layout was changed;
@@ -146,6 +157,10 @@ gpg_disable_sign: false
 # Disable signature verification of remote repositories
 gpg_disable_verify: false
 
+# GPG key IDs to sign with when a publish does not name one itself
+# (the -gpg-key flag, or GpgKey in the API's signing options)
+gpg_keys: []
+
 
 # Publishing
 #############