Document semver-ish versioning (#1638)

Author: yorickdowne

README.md

@@ -29,4 +29,9 @@ please read the [contribution guidelines](CONTRIBUTING.md) so you can run lint c
 
 ## Version
 
-This is Eth Docker v2.3.9
+Eth Docker uses a "semver-ish" scheme.
+- First digit, major shifts in how things work. The last one was Ethereum merge. I do not expect another shift that
+large.
+- Second through fourth digit, [semver](https://semver.org/).
+
+This is Eth Docker v2.3.10.0

default.env

@@ -164,7 +164,7 @@ MEV_NODE=http://mev-boost:18550
 # The default source build targets build from the latest github tag
 
 # Eth Docker updates its code to latest by default.
-# Set a github tag here to pin it to a version.
+# Set a Github tag here to pin it to a version. Supported from v2.3.9.
 ETH_DOCKER_TAG=
 
 # SSV