Copy edit issue_template.md

Make minor copy edits for grammar.

Author: Amanda Butler

.github/issue_template.md

@@ -2,10 +2,10 @@
 
 <!-- 
     Required
-    Please add only one X to one of the following types. Do not fill multiple types (split the issue otherwise)
-    Please note this is not a GitHub task list, indenting the boxes or changing the format to add a '.' or '*' in front
-    of them would change the meaning incorrectly. The only changes to be made are to add a description text under the
-    description heading and to add a 'x' to the correct box.
+    Please add only one X to one of the following types. Do not fill multiple types. (Split the issue otherwise.)
+    Please note this is not a GitHub task list; indenting the boxes or changing the format to add a '.' or '*' in front
+    of them changes the meaning incorrectly. The only changes to make are to add a description under the
+    description heading and to add an 'x' to the correct box.
 
     [X] Question
     [ ] Enhancement 
@@ -18,12 +18,12 @@
 
 <!-- 
     Required
-    Add detailed description of what is being reported
+    Add detailed description of what you are reporting.
     Good example: https://os.mbed.com/docs/latest/reference/workflow.html
     Things to consider sharing:
     - What target does this relate to?
-    - What toolchain is being used?
+    - What toolchain are you using?
     - What is the SHA of Mbed OS (git log -n1 --oneline)?
-    - Steps to reproduce (Did you publish code or a test case that exhibits the problem)
+    - Steps to reproduce. (Did you publish code or a test case that exhibits the problem?)
 -->
 ### Description