doc: Bump minimum Compose version requirement to 1.26.0

Prior to this version, surrounding quotes (single and double) were
preserved in values coming from the '.env' file, which is counter
intuitive and goes against the recommended practice of quoting values
containing special characters, such as passwords.

Closes #677

README.md

@@ -76,7 +76,7 @@ own_. [sherifabdlnaby/elastdocker][elastdocker] is one example among others of p
 ### Host setup
 
 * [Docker Engine](https://docs.docker.com/install/) version **18.06.0** or newer
-* [Docker Compose](https://docs.docker.com/compose/install/) version **1.22.0** or newer
+* [Docker Compose](https://docs.docker.com/compose/install/) version **1.26.0** or newer
 * 1.5 GB of RAM
 
 *:information_source: Especially on Linux, make sure your user has the [required permissions][linux-postinstall] to