Update README.

README.md

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-# gemfeed
+# Gemfeed
 
-Generate an Atom feed from a directory of text/gemini files.
+Gemfeed is a simple tool for generating Atom feeds for directories of
+text/gemini files.  It may not be adequate for large, complicated
+Gemini sites, but if you have, for example, a gemlog which is just a
+single directory full of .gmi files, each of which corresponds to one
+post, then the idea is that you can call gemfeed from a regular
+cronjob (or by hand after you write each post, if you like!) and
+maintain an Atom feed for your gemlog with very little extra effort.
+
+Basically, when run Gemfeed will find all world-readable `.gmi` or
+`.gemini` files in the current directory and add the 10 most recently
+created ones to an Atom feed it will save to the file `atom.xml`.
+
+* Each file's creation time will be used as the corresponding entry's
+  update time.
+* The first heading line in each file (i.e. the first line encountered
+  which begins with `#`, `##` or `###`) will be used as the
+  corresponding entry's title.  If your file contains no heading line,
+  the filename will be used as a title instead, with its extension
+  removed.
+* If an `index.gmi` or `index.gemini` file is found, it won't be
+  included as an entry in the feed, but the first heading line in the
+  index file will be used as the title for the feed.  If your index
+  file contains no heading line, you'll get the dorky default "Just
+  another Gemini feed".
+
+The only information you *need* to provide to make this happen is a
+base URL (with `-b` or `--base`).  If you provide a base URL of
+`gemini://example.org/my-gemlog/` then Gemfeed will assume that a
+file it finds named `my-first-post.gmi` is accessible via the URL
+`gemini://example.org/my-gemlog/my-first-post.gmi`, and that the file
+it produces will be accessible via the URL
+`gemini://example.org/my-gemlog/atom.xml`.  Basically, you should
+provide the URL which will your server will map to the directory
+you're trying to generate a feed for.
+
+If you want to, you can provide additional information above and
+beyond the base URL:
+
+* You can specify a directory other than the present working directory
+  with `-d` or `--directory`.
+* You can specify a number of posts other than 10 with `-n`
+* You can change the output filename with `-o` or `--output`.
+* You can specify your own feed title and subtitle with `-t` or
+  `--title` and `-s` or `--subtitle`, respectively.  If you specify a
+  title, it will override any heading line in your index file.
+* You can specify an author name for the feed with `-a` or `--author`
+  and/or an author email address for the feed with `-e` or `--email`.
+* If you specify `-q` or `--quiet`, Gemfeed will write nothing to
+  stdout unless there's a problem - ideal for cron jobs!