Add --global (-g) flag (#1029)

This will run a Taskfile from the home directory, i.e., `$HOME/Taskfile.yml`.

docs/docs/api_reference.md

@@ -28,6 +28,7 @@ variable
 | `-n` | `--dry` | `bool` | `false` | Compiles and prints tasks in the order that they would be run, without executing them. |
 | `-x` | `--exit-code` | `bool` | `false` | Pass-through the exit code of the task command. |
 | `-f` | `--force` | `bool` | `false` | Forces execution even when the task is up-to-date. |
+| `-g` | `--global` | `bool` | `false` | Runs global Taskfile, from `$HOME/Taskfile.{yml,yaml}`. |
 | `-h` | `--help` | `bool` | `false` | Shows Task usage. |
 | `-i` | `--init` | `bool` | `false` | Creates a new Taskfile.yaml in the current folder. |
 | `-I` | `--interval` | `string` | `5s` | Sets a different watch interval when using `--watch`, the default being 5 seconds. This string should be a valid [Go Duration](https://pkg.go.dev/time#ParseDuration). |

docs/docs/usage.md

@@ -81,6 +81,40 @@ In this example, we can run `cd <service>` and `task up` and as long as the
 `<service>` directory contains a `docker-compose.yml`, the Docker composition will be
 brought up.
 
+### Running a global Taskfile
+
+If you call Task with the `--global` (alias `-g`) flag, it will look for your
+home directory instead of your working directory. In short, Task will look for
+a Taskfile on either `$HOME/Taskfile.yml` or `$HOME/Taskfile.yaml` paths.
+
+This is useful to have automation that you can run from anywhere in your
+system!
+
+:::info
+
+When running your global Taskfile with `-g`, tasks will run on `$HOME` by
+default, and not on your working directory!
+
+As mentioned in the previous section, the `{{.USER_WORKING_DIR}}` special
+variable can be very handy here to run stuff on the directory you're calling
+`task -g` from.
+
+```yaml
+version: '3'
+
+tasks:
+  from-home:
+    cmds:
+      - pwd
+
+  from-working-directory:
+    dir: '{{.USER_WORKING_DIR}}'
+    cmds:
+      - pwd
+```
+
+:::
+
 ## Environment variables
 
 ### Task