docs: Update templated markdown docs to use new default branch name

Author: twilio-ci

ISSUE_TEMPLATE.md

@@ -1,5 +1,9 @@
 <!--
 If this is a feature request, make sure you search Issues for an existing request before creating a new one!
+
+Please utilize the template below to help us resolve your issue.
+
+Note that many issues can be resolved by updating to the latest version.
 -->
 
 ### Issue Summary
@@ -21,6 +25,6 @@ A summary of the issue and the environment in which it occurs. If suitable, incl
 ```
 
 ### Technical details:
-* sendgrid-csharp version:
+* sendgrid-csharp version: 
 * csharp version:
 

PULL_REQUEST_TEMPLATE.md

@@ -23,7 +23,7 @@ A short description of what this PR does.
 - [ ] I have made a material change to the repo (functionality, testing, spelling, grammar)
 - [ ] I have read the [Contribution Guidelines](CONTRIBUTING.md) and my PR follows them
 - [ ] I have titled the PR appropriately
-- [ ] I have updated my branch with the master branch
+- [ ] I have updated my branch with the main branch
 - [ ] I have added tests that prove my fix is effective or that my feature works
 - [ ] I have added necessary documentation about the functionality in the appropriate .md file
 - [ ] I have added inline documentation to the code I modified