Add a default alternate suffix of `##`

Now yadm chooses these three suffixes in order:
 - `##SYSTEM.HOSTNAME`
 - `##SYSTEM`
 - `##`

yadm

@@ -107,7 +107,7 @@ function alt() {
   #; regex for matching "<file>##SYSTEM.HOSTNAME"
   match_system=$(uname -s)
   match_host=$(hostname -s)
-  match="^(.+)##($match_system|$match_system.$match_host)$"
+  match="^(.+)##($match_system|$match_system.$match_host|())$"
 
   #; process relative to YADM_WORK
   YADM_WORK=$(git config core.worktree)

yadm.1

@@ -247,10 +247,10 @@ implements a feature which will automatically create a symbolic link to
 the appropriate version of a file, as long as you follow a specific naming
 convention.
 .B yadm
-can detect files with names ending with:
+can detect files with names ending in:
 
 .RS
-.BR ##SYSTEM " or " ##SYSTEM.HOSTNAME
+.BR ##OS.HOSTNAME " or " ##OS " or " ##
 .RE
 
 If there are any files managed by
@@ -261,6 +261,7 @@ This may best be demonstrated by example. Assume the following files are managed
 .BR yadm \'s
 repository:
 
+  - $HOME/path/example.txt##
   - $HOME/path/example.txt##Darwin
   - $HOME/path/example.txt##Darwin.host1
   - $HOME/path/example.txt##Darwin.host2
@@ -282,16 +283,19 @@ will create a symbolic link which looks like this:
 
 Since the hostname doesn't match any of the managed files, the more generic version is chosen.
 
-If running on a Linux server named "host4" the link will be:
+If running on a Linux server named "host4", the link will be:
 
 .IR $HOME/path/example.txt " -> " $HOME/path/example.txt##Linux
 
-If running on a Solaris server, no link will be created because there are no
-files managed for that SYSTEM.
+If running on a Solaris server, the link use the default "##" version:
 
-SYSTEM is determined by running
-.B uname\ -s
-HOSTNAME by running
+.IR $HOME/path/example.txt " -> " $HOME/path/example.txt##
+
+If no "##" version exists and no files match the current OS or HOSTNAME, then no link will be created.
+
+OS is determined by running
+.BR uname\ -s ,
+and HOSTNAME by running
 .BR hostname\ -s .
 .B yadm
 will automatically create these links by default. This can be disabled using the

yadm.md

@@ -149,15 +149,16 @@
        a  different  operation  system  or  simply for a different host.  yadm
        implements a feature which will automatically create a symbolic link to
        the  appropriate  version  of  a file, as long as you follow a specific
-       naming convention.  yadm can detect files with names ending with:
+       naming convention.  yadm can detect files with names ending in:
 
-              ##SYSTEM or ##SYSTEM.HOSTNAME
+              ##OS.HOSTNAME or ##OS or ##
 
        If there are any files managed by yadm's repository  which  match  this
        naming  convention,  symbolic links will be created for the most appro-
        priate version.  This may best be demonstrated by example.  Assume  the
        following files are managed by yadm's repository:
 
+         - $HOME/path/example.txt##
          - $HOME/path/example.txt##Darwin
          - $HOME/path/example.txt##Darwin.host1
          - $HOME/path/example.txt##Darwin.host2
@@ -178,14 +179,18 @@
        Since  the  hostname  doesn't  match any of the managed files, the more
        generic version is chosen.
 
-       If running on a Linux server named "host4" the link will be:
+       If running on a Linux server named "host4", the link will be:
 
        $HOME/path/example.txt -> $HOME/path/example.txt##Linux
 
-       If running on a Solaris server, no link will be created  because  there
-       are no files managed for that SYSTEM.
+       If running on a Solaris server, the link use the default "##" version:
 
-       SYSTEM  is  determined  by  running  uname -s HOSTNAME by running host-
+       $HOME/path/example.txt -> $HOME/path/example.txt##
+
+       If no "##" version exists and no files match the current  OS  or  HOST-
+       NAME, then no link will be created.
+
+       OS  is  determined  by  running uname -s, and HOSTNAME by running host-
        name -s.  yadm will automatically create these links by  default.  This
        can  be  disabled  using the yadm.auto-alt configuration.  Even if dis-
        abled, links can be manually created by running yadm alt.