Document --change-time in web-based docs' command line reference (#1471)

* Document change-time in command line reference
* Keep mkdocs version under 1.3 both locally and for readthedocs

pyproject.toml

@@ -51,7 +51,7 @@ pytest-bdd =  { version = ">=4.0.1",  optional = true }
 toml       =  { version = ">=0.10",   optional = true }
 
 [tool.poetry.dev-dependencies]
-mkdocs = ">=1.0"
+mkdocs = ">=1.0,<1.3"
 black = { version = ">=21.5b2", allow-prereleases = true }
 toml = ">=0.10"
 pytest = ">=6.2"