Dev guide manifest section: address review actions. Re nvaccess#8593.

Reviewed by Derek Riemer and James Scholes: when mentioning string type, also mention the fact that it must be enclosed in quotes. For the example manifest, quoted all striong values. In addition, docFileName now has an example.

developerGuide.t2t

@@ -654,24 +654,25 @@ This manifest file contains key = value pares declaring info such as the add-on'
 +++ Available Fields +++
 Although it is highly suggested that manifests contain all fields, the fields marked as mandatory must be included.
 Otherwise, the add-on will not install.  
-- name (string): A short unique name for the add-on. This is used to differentiate add-ons internally and is not shown to the user. (Mandatory)
+- name (string enclosed in quotes): A short unique name for the add-on. This is used to differentiate add-ons internally and is not shown to the user. (Mandatory)
 - summary (string enclosed in quotes): The name of the add-on as shown to the user. (Mandatory)
 - description (string enclosed in quotes): A sentence or two describing what the add-on does. If this spans multiple lines, you need to enclose this information in triple quotes (""").
-- version (string): The version of this add-on; e.g. 2.0. (Mandatory)
+- version (string enclosed in quotes): The version of this add-on; e.g. 2.0. (Mandatory)
 - author (string enclosed in quotes): The author of this add-on, preferably in the form Full Name <email address>; e.g. Michael Curran <mick@kulgan.net>. (Mandatory)
-- url (string): A URL where this add-on, further info and upgrades can be found.
-- docFileName (string): The name of the main documentation file for this add-on; e.g. readme.html. See the [Add-on Documentation #AddonDoc] section for more details.
+- url (string enclosed in quotes): A URL where this add-on, further info and upgrades can be found.
+- docFileName (string enclosed in quotes): The name of the main documentation file for this add-on; e.g. readme.html. See the [Add-on Documentation #AddonDoc] section for more details.
 -
 
 +++ An Example Manifest File +++
 ```
 --- start ---
-name = MyTestAddon
+name = "myTestAddon"
 summary = "Cool Test Add-on"
-version = 1.0
+version = "1.0"
 description = "An example add-on showing how to create add-ons!"
 author = "Michael Curran <mick@kulgan.net>"
-url = http://www.nvda-project.org/wiki/Development
+url = "http://www.nvda-project.org/wiki/Development"
+docFileName = "readme.html"
 --- end ---
 ```