[llvm][Docs] Update MyFirstTypoFix doc (#79149)

I've not tried to change the purpose or style of the doc, just edited
for clarity and removed any Phabricator related language in favour of
GitHub terms.

Where possible, I've swapped direct links to LLVM's website with RST
links to the local documents. Which should be a bit more resilient.

Also it's less confusing if you're editing multiple pages locally, you
don't accidentally end up on the live site.

Author: DavidSpickett

llvm/docs/CodeReview.rst

@@ -1,3 +1,5 @@
+.. _code_review_policy:
+
 =====================================
 LLVM Code-Review Policy and Practices
 =====================================

llvm/docs/DeveloperPolicy.rst

@@ -1,3 +1,5 @@
+.. _developer_policy:
+
 =====================
 LLVM Developer Policy
 =====================
@@ -469,6 +471,8 @@ What are the expectations around a revert?
 * When re-applying a reverted patch, the commit message should be updated to
   indicate the problem that was addressed and how it was addressed.
 
+.. _obtaining_commit_access:
+
 Obtaining Commit Access
 -----------------------
 

llvm/docs/GettingStarted.rst

@@ -330,6 +330,8 @@ Unix utilities. Specifically:
 .. _below:
 .. _check here:
 
+.. _host_cpp_toolchain:
+
 Host C++ Toolchain, both Compiler and Standard Library
 ------------------------------------------------------