Document how to ignore errors with - in readme (#690)

.github/workflows/build.yaml

@@ -14,7 +14,7 @@ env:
   # Increment to invalidate github actions caches if they become corrupt.
   # Errors of the form "can't find crate for `snafu_derive` which `snafu` depends on"
   # can usually be fixed by incrementing this value.
-  CACHE_KEY_PREFIX: 2
+  CACHE_KEY_PREFIX: 3
 
 jobs:
   all:

README.adoc

@@ -437,6 +437,26 @@ string!
 "
 ```
 
+=== Ignoring Errors
+
+Normally, if a command returns a nonzero exit status, execution will stop. To
+continue execution after a command, even if it fails, prefix the command with
+`-`:
+
+```make
+foo:
+    cat foo
+    echo 'Done!'
+```
+
+```sh
+$ just foo
+cat foo
+cat: foo: No such file or directory
+echo 'Done!'
+Done!
+```
+
 === Functions
 
 Just provides a few built-in functions that might be useful when writing recipes.