feat(docs): explain the tox environments

Author: gforcada

config/README.md

@@ -377,6 +377,9 @@ _custom configuration_
 
 ### `tox.ini`
 
+
+#### Testing
+
 Depending on the test runner that you want to use,
 `plone/meta` will adapt `tox.ini` to it.
 
@@ -390,6 +393,23 @@ and thus the tests can be found directly.
 
 If either a `tests` or `src` folder exists, then they are used as a safe fallbacks.
 
+#### Environments
+
+`plone/meta` generates the following `tox` environments:
+
+- `init`: prepares the environment (only if `mxdev` is used)
+- `test`: runs the package's python tests
+- `coverage`: runs the package's python tests and generates a coverage report out of it
+- `dependencies`: checks that all python dependencies are specified properly
+- `dependencies-graph`: generates a graph to visualize the dependencies tree/forest
+- `circular`: checks that within the dependency graph there are no circular imports
+- `release-check`: runs a few sanity checks to know if the distribution is ready to be released
+- `release`: releases a new version of the distribution
+- `format`: runs python/HTML/XML code formatters on the source code
+- `lint`: runs quite some python linters
+
+#### Options
+
 Add the `[tox]` TOML table in `.meta.toml`,
 and set the extra configuration for `tox` under the `extra_lines` key.