Add --cache-fine-grained to docs (python#4685)

This was discovered in python#4403. I thought I'd add it while I am splitting changes out of that PR. It was originally introduced in python#4526 but not added to the docs it seems.

(the rest of the diff is due to my using an actual output of the help command from master)

docs/source/command_line.rst

@@ -11,14 +11,17 @@ flag (or its long form ``--help``)::
   usage: mypy [-h] [-v] [-V] [--python-version x.y] [--platform PLATFORM] [-2]
               [--ignore-missing-imports]
               [--follow-imports {normal,silent,skip,error}]
-              [--disallow-any-{unimported,expr,decorated,explicit,generics}]
-              [--disallow-untyped-calls] [--disallow-untyped-defs]
+              [--disallow-any-unimported] [--disallow-any-expr]
+              [--disallow-any-decorated] [--disallow-any-explicit]
+              [--disallow-any-generics] [--disallow-untyped-calls]
+              [--disallow-untyped-defs] [--disallow-incomplete-defs]
               [--check-untyped-defs] [--disallow-subclassing-any]
-              [--warn-incomplete-stub] [--warn-redundant-casts]
-              [--no-warn-no-return] [--warn-return-any] [--warn-unused-ignores]
+              [--warn-incomplete-stub] [--disallow-untyped-decorators]
+              [--warn-redundant-casts] [--no-warn-no-return] [--warn-return-any]
+              [--warn-unused-ignores] [--warn-unused-configs]
               [--show-error-context] [--no-implicit-optional] [-i]
-              [--quick-and-dirty] [--cache-dir DIR] [--skip-version-check]
-              [--strict-optional]
+              [--quick-and-dirty] [--cache-dir DIR] [--cache-fine-grained]
+              [--skip-version-check] [--strict-optional]
               [--strict-optional-whitelist [GLOB [GLOB ...]]]
               [--junit-xml JUNIT_XML] [--pdb] [--show-traceback] [--stats]
               [--inferstats] [--custom-typing MODULE]
@@ -28,9 +31,9 @@ flag (or its long form ``--help``)::
               [--shadow-file SOURCE_FILE SHADOW_FILE] [--any-exprs-report DIR]
               [--cobertura-xml-report DIR] [--html-report DIR]
               [--linecount-report DIR] [--linecoverage-report DIR]
-              [--memory-xml-report DIR]
-              [--txt-report DIR] [--xml-report DIR] [--xslt-html-report DIR]
-              [--xslt-txt-report DIR] [-m MODULE] [-c PROGRAM_TEXT] [-p PACKAGE]
+              [--memory-xml-report DIR] [--txt-report DIR] [--xml-report DIR]
+              [--xslt-html-report DIR] [--xslt-txt-report DIR] [-m MODULE]
+              [-c PROGRAM_TEXT] [-p PACKAGE]
               [files [files ...]]
 
   (etc., too long to show everything here)