Update README.org (syl20bnr#15657)

layers/+lang/plantuml/README.org

@@ -42,31 +42,41 @@ For example, the following diagram can be defined as follows:
 - Controlling the =Plantuml= compiler directly from emacs
 
 * Install
-To use this contribution add it to your =~/.spacemacs=
+To use this contribution, add it to your =~/.spacemacs=
 
 #+BEGIN_SRC emacs-lisp
   (setq-default dotspacemacs-configuration-layers '(plantuml))
 #+END_SRC
 
-To control the =Plantuml= compiler you also need to download the [[http://plantuml.com/download][Plantuml jar]]
-and configure the =plantuml-jar-path= respectively:
+** Execution modes
 
+Configure plantuml-mode to either make use of a =Plantuml= library, executable or server (experimental).
+
+If you want to call your local Plantuml library, set =plantuml-jar-path= and =plantuml-default-exec-mode= as follows:
 #+BEGIN_SRC emacs-lisp
-  (setq-default dotspacemacs-configuration-layers '((plantuml :variables plantuml-jar-path "~/plantUml.jar")))
+(setq-default dotspacemacs-configuration-layers '((plantuml :variables 
+    plantuml-jar-path "~/plantUml.jar"
+    plantuml-default-exec-mode 'library)))
 #+END_SRC
+For this to work, you need to execute =plantuml-download-jar= to download the most recent =Plantuml= library jar to your home directory.
 
-To get the full range of =Plantuml= compilations working, you will also need
-the native package [[http://graphviz.org/][graphviz]] installed on your system.
+If instead you want to call your local Plantuml executable (f.e. as installed to path =/usr/bin/plantuml= by your package manager), set =plantuml-executable-path= and =plantuml-default-exec-mode= as follows:
+#+BEGIN_SRC emacs-lisp
+(setq-default dotspacemacs-configuration-layers '((plantuml :variables 
+    plantuml-executable-path "/usr/bin/plantuml"
+    plantuml-default-exec-mode 'executable)))
+#+END_SRC
 
-If you don't want to compile locally you can set =plantuml-exec-mode= to =server=.
-This will make plantuml try to use an online compile server. Be warned these resources
-change often and plantuml-mode is not always up-to-date. For a stable user experience
-we recommend using the default jar option instead.
+If instead you don't want to compile locally, you can set =plantuml-exec-mode= to =server=.
+This will make plantuml try to use an online compile server. Be warned that this feature is experimental.
 
 #+BEGIN_SRC emacs-lisp
   (setq-default dotspacemacs-configuration-layers '((plantuml :variables plantuml-default-exec-mode 'server)))
 #+END_SRC
 
+Either way, to get the full range of =Plantuml= compilations working, you will also need
+the native package [[http://graphviz.org/][graphviz]] installed on your system.
+
 * Org-Babel Integration
 To enable the execution of embedded plantuml code blocks within [[http://orgmode.org/][Org-Mode]]
 documents, define a value for =org-plantuml-jar-path= in your =~/.spacemacs=: