USMT/XML General Conventions: fix example typo

Description:

As suggested in issue ticket #5603
(USMT XML Ref typo - File.txt => file].txt),
the example filename should contain the aforementioned bracket
that this section is all about, as well as preferably use the same case
(lowercase) as the directly following XML code.

Thanks to ChadMcCaffery for reporting this typo.

Changes proposed:

- add the missing example bracket character
- convert the filename "File" to lowercase "file"
- add bold text for the filename to be more visible

issue ticket closure or reference:

Closes #5603

windows/deployment/usmt/usmt-general-conventions.md

@@ -50,7 +50,7 @@ Before you modify the .xml files, become familiar with the following guidelines:
     -   The required child elements apply only to the first definition of the element. If these elements are defined and then referred to using their name, the required child elements do not apply. For example, if you define `<detects name="Example">` in **&lt;namedElements&gt;**, and you specify `<detects name="Example"/>` in **&lt;component&gt;** to refer to this element, the definition inside **&lt;namedElements&gt;** must have the required child elements, but the **&lt;component&gt;** element does not need to have the required child elements.
 
 -   **File names with brackets**
-
+
     If you are migrating a file that has a bracket character (\[ or \]) in the file name, you must insert a carat (^) character directly before the bracket for the bracket character to be valid. For example, if there is a file named **file].txt**, you must specify `<pattern type="File">c:\documents\mydocs [file^].txt]</pattern>` instead of `<pattern type="File">c:\documents\mydocs [file].txt]</pattern>`.
 
 -   **Using quotation marks**