DOC: config: move the cache-use and cache-store actions to the proper section

Actions were grouped by previous commit d54e8f810 ("DOC: config: reorganize
actions into their own section") but cache-use and cache-store were still
making reference to the cache section. This moves the text back to their
respective keywords in the actions section and leaves the example and an
explanation of how to use the keywords in the cache section.

doc/configuration.txt

@@ -12960,6 +12960,11 @@ cache-store <name>
   Usable in:  TCP RqCon| RqSes| RqCnt| RsCnt|    HTTP Req| Res| Aft
                     -  |   -  |   -  |   -  |          - |  X |  -
 
+  Store an http-response within the cache. The storage of the response headers
+  is done at this step, which means you can use others http-response actions
+  to modify headers before or after the storage of the response. This action
+  is responsible for the setup of the cache storage filter.
+
   See section 6.2 about cache setup.
 
 
@@ -12967,6 +12972,11 @@ cache-use <name>
   Usable in:  TCP RqCon| RqSes| RqCnt| RsCnt|    HTTP Req| Res| Aft
                     -  |   -  |   -  |   -  |          X |  - |  -
 
+  Try to deliver a cached object from the cache <name>. This directive is also
+  mandatory to store the cache as it calculates the cache hash. If you want to
+  use a condition for both storage and delivering that's a good idea to put it
+  after this one.
+
   See section 6.2 about cache setup.
 
 
@@ -16705,7 +16715,7 @@ The cache won't store and won't deliver objects in these cases:
 -----------
 
 To setup a cache, you must define a cache section and use it in a proxy with
-the corresponding http-request and response actions.
+the corresponding http-request and http-response actions.
 
 
 6.2.1. Cache section
@@ -16749,18 +16759,16 @@ max-secondary-entries <number>
 6.2.2. Proxy section
 ---------------------
 
-http-request cache-use <name> [ { if | unless } <condition> ]
-  Try to deliver a cached object from the cache <name>. This directive is also
-  mandatory to store the cache as it calculates the cache hash. If you want to
-  use a condition for both storage and delivering that's a good idea to put it
-  after this one.
-
-http-response cache-store <name> [ { if | unless } <condition> ]
-  Store an http-response within the cache. The storage of the response headers
-  is done at this step, which means you can use others http-response actions
-  to modify headers before or after the storage of the response. This action
-  is responsible for the setup of the cache storage filter.
-
+The proxy section making use of the cache will need to involve the "cache-use"
+action in the "http-request" rule set in order to look up the requested object
+from the cache, and the "cache-store" action in the "http-response" rule set in
+order to store or update the retrieved object into the cache. Each of these
+actions may optionally involve conditions. For example, one could decide to
+skip the "cache-use" action for a certain sub-directory that is known not to
+be cacheable, or to skip the "cache-store" action for certain content-types
+that are known to be worthless. Please note that the cache indexing key is
+computed during the "cache-use" action, so if this action is skipped, no
+attempt to update the cache will be made on the response path anyway.
 
 Example: