Update docs/docker.md

Co-authored-by: Martin Stone <[email protected]>

docs/docker.md

@@ -6,9 +6,10 @@ The following tags are available:
 
 * `latest`: Latest Lychee release
 * `v[NUMBER]`: Stable version tag for a Lychee release
-* `dev` or `nightly` : Current master branch tag (Lychee operates on a stable master, so this should usually be safe)
-* `devtools` : Same as `dev` but with the developper extensions enabled (e.g. api docs, debug bar...).
-* `alpha`: Same as `dev` but uses the alpha branch instead (contains merged pull request without peer review).
+* `nightly` (also `dev`): Current master branch tag (Lychee operates on a stable master, so this should usually be safe)
+* `devtools`: Same as `nightly`, but includes development dependencies (e.g. api docs, debug bar)
+* `alpha`: Current alpha branch tag (The alpha branch contains bleeding edge changes that are not peer-reviewed)
+* `alpha-devtools`: Same as `alpha`, but includes development dependencies  (e.g. api docs, debug bar)
 * `testing`: Tag for testing new branches and pull requests. Designed for internal use by LycheeOrg.
 
 Note that only the `:dev` tag is available for armv6 and armv7 systems. This is due to an issue with the build environment and is hopefully temporary.