Add note about HACS to readme

Author: pnbruckner

README.md

@@ -18,6 +18,7 @@ device_tracker:
 ```
 
 ## Installation
+### Manual
 
 Place a copy of:
 
@@ -30,6 +31,9 @@ where `<config>` is your Home Assistant configuration directory.
 
 >__NOTE__: Do not download the file by using the link above directly. Rather, click on it, then on the page that comes up use the `Raw` button.
 
+### With HACS
+You can use [HACS](https://hacs.xyz/) to manage installation and updates by adding this repo as a [custom repository](https://hacs.xyz/docs/faq/custom_repositories/) and then searching for and installing the "Composite" integration.
+
 ### numpy on Raspberry Pi
 
 To determine time zone from GPS coordinates (see `time_as` configuration variable below) the package [timezonefinderL](https://pypi.org/project/timezonefinderL/) (by default) is used. That package requires the package [numpy](https://pypi.org/project/numpy/). These will both be installed automatically by HA. Note, however, that numpy on Pi _usually_ requires libatlas to be installed. (See [this web page](https://www.raspberrypi.org/forums/viewtopic.php?t=207058) for more details.) It can be installed using this command: