Document that editors must be blocking processes (#1624)

* Describe blocking processes in External Editors page
* Add documentation about how the editor must be a blocking process
* Add contextual link to external editor site
* Point to micro editor as an example since it's likely less intimidating than vim

docs/external-editors.md

@@ -8,11 +8,13 @@ License: https://www.gnu.org/licenses/gpl-3.0.html
 Configure your preferred external editor by updating the `editor` option
 in your [configuration file](./reference-config-file.md#editor)
 
+If your editor is not in your operating system's `PATH` environment variable,
+then you will have to enter in the full path of your editor.
+
 !!! note
     To save and log any entry edits, save and close the file.
 
-If your editor is not in your operating system's `PATH` environment variable,
-then you will have to enter in the full path of your editor.
+All editors must be [blocking processes](https://en.wikipedia.org/wiki/Blocking_(computing)) to work with jrnl. Some editors, such as [micro](https://micro-editor.github.io/), are blocking by default, though others can be made to block with additional arguments, such as many of those documented below. If jrnl opens your editor but finishes running immediately, then your editor is not a blocking process, and you may be able to correct that with one of the suggestions below.
 
 ## Sublime Text
 

docs/reference-config-file.md

@@ -47,10 +47,11 @@ key will be used instead.
 If set, executes this command to launch an external editor for
 writing and editing your entries. The path to a temporary file
 is passed after it, and `jrnl` processes the file once
-the editor is closed.
+the editor returns control to `jrnl`.
 
-Some editors require special options to work properly. See
-[External Editors](external-editors.md) for details.
+Some editors require special options to work properly, since they must be
+blocking processes to work with `jrnl`. See [External Editors](external-editors.md)
+for details.
 
 ### encrypt
 If `true`, encrypts your journal using AES. Do not change this