Updates README with information about layouts

README.md

@@ -103,6 +103,76 @@ gotop ships with a few colorschemes which can be set with the `-c` flag followed
 
 To make a custom colorscheme, check out the [template](./colorschemes/template.go) for instructions and then use [default.json](./colorschemes/default.json) as a starter. Then put the file at `~/.config/gotop/<name>.json` and load it with `gotop -c <name>`. Colorschemes PR's are welcome!
 
+### Layouts
+
+gotop can parse and render layouts from a specification file.  The format is
+intentionally simple.  The amount of nesting levels is limited.  Some examples
+are in the `layouts` directory; you can try each of these with, e.g.,
+`gotop --layout-file layouts/procs`.  If you stick your layouts in
+`$XDG_CONFIG_HOME/gotop`, you can reference them on the command line with the
+`-l` argument, e.g. `gotop -l procs`.
+
+The syntax for each widget in a row is:
+```
+(rowspan:)?widget(/weight)?
+```
+and these are separated by spaces.
+
+1. Each line is a row
+2. Empty lines are skipped
+3. Spaces are compressed (so you can do limited visual formatting)
+4. Legal widget names are: cpu, disk, mem, temp, batt, net, procs
+5. Widget names are not case sensitive
+4. The simplest row is a single widget, by name, e.g.
+   ```
+   cpu
+   ```
+5. **Weights**
+    1. Widgets with no weights have a weight of 1.
+    2. If multiple widgets are put on a row with no weights, they will all have
+       the same width.
+    3. Weights are integers
+    4. A widget will have a width proportional to its weight divided by the
+       total weight count of the row. E.g.,
+       ```
+       cpu      net
+       disk/2   mem/4
+       ```
+       The first row will have two widgets: the CPU and network widgets; each
+       will be 50% of the total width wide.  The second row will have two
+       widgets: disk and memory; the first will be 2/6 ~= 33% wide, and the
+       second will be 5/7 ~= 67% wide (or, memory will be twice as wide as disk).
+9. If prefixed by a number and colon, the widget will span that number of
+   rows downward. E.g.
+   ```
+   mem   2:cpu
+   net
+   ```
+   Here, memory and network will be in the same row as CPU, one over the other,
+   and each half as high as CPU; it'll look like this:
+   ```
+    +------+------+
+    | Mem  |      |
+    +------+ CPU  |
+    | Net  |      |
+    +------+------+
+   ```
+10. Negative, 0, or non-integer weights will be recorded as "1".  Same for row
+    spans. 
+11. Unrecognized widget names will cause the application to abort.                          
+12. In rows with multi-row spanning widgets **and** weights, weights in
+    lower rows are ignored.  Put the weight on the widgets in that row, not
+    in later (spanned) rows.
+13. Widgets are filled in top down, left-to-right order.
+14. The larges row span in a row defines the top-level row span; all smaller
+    row spans constitude sub-rows in the row. For example, `cpu mem/3 net/5`
+    means that net/5 will be 5 rows tall overall, and mem will compose 3 of
+    them. If following rows do not have enough widgets to fill the gaps,
+    spacers will be used.
+
+Yes, you're clever enough to break the layout algorithm, but if you try to
+build massive edifices, you're in for disappointment.
+
 ### CLI Options
 
 `-c`, `--color=NAME` Set a colorscheme.