Document stack hoogle command

Author: mpilgrem

doc/hoogle_command.md

@@ -7,4 +7,27 @@ stack hoogle [-- ARGUMENT(S) (e.g. 'stack hoogle -- server --local')]
              [--[no-]setup] [--rebuild] [--server]
 ~~~
 
-Hoogle is a Haskell API search engine. `stack hoogle` runs Hoogle.
+Hoogle is a Haskell API search engine. `stack hoogle` runs Hoogle. Stack needs
+Hoogle version 5 or greater.
+
+Stack will use a Hoogle database (`database.hoo`) specific to the project's
+source map and the version of GHC, located in a subdirectory of subdirectory
+`hoogle` of Stack's work directory for the project.
+
+By default:
+
+*   if a `hoogle` executable is found on the `PATH`, Stack will try to use it.
+    Otherwise, Stack will try to identify an executable as a build target. If
+    the Hoogle database does not exist, Stack will generate it with
+    `hoogle generate --local`. `hoogle generate --local` queries `ghc-pkg` and
+    generates links for all packages which have documentation and Hoogle input
+    files (`*.txt`) generated. Pass the flag `--no-setup` to skip such setup;
+
+*   the existing Hoogle database is used. Pass the flag `--rebuild` to trigger
+    the generation of a new Hoogle database (generated as above); and
+
+*   `hoogle` is passed the specified arguments (if any). The arguments are
+    usually the subject of the search. Pass the flag `--server` to first pass
+    `server --local --port 8080` before those arguments.
+    `hoogle server --local --port 8080` starts a local Hoogle web server, using
+    port 8080, that allows the following of `file://` links.