Add some docs

Documentation/guides/messages/README.md

@@ -40,6 +40,9 @@
 
 ### XA1xxx Project Related
 
++ [XA1000](xa1000.md): We found a matching key '{Key}' for '{Item}'. But the casing was incorrect. Please correct the casing
++ [XA1001](xa1001.md): AndroidResgen: Warning while updating Resource XML '{filename}': {Message}
+
 ### XA2xxx Linker
 
 ### XA3xxx AOT
@@ -59,4 +62,4 @@
 
 ### XA8xxx	Reserved
 
-### XA9xxx	Licensing
+### XA9xxx	Licensing

Documentation/guides/messages/xa1000.md

@@ -0,0 +1,13 @@
+# Compiler Error XA1000
+
+This error will be emitted when we are unable to find a matching custom new in the 
+ResourceCaseMap string. 
+
+As part of the build process `Namespace.CustomViewFoo` items in layout files are
+replaced with `{MD5Hash}.CustomViewFoo`. We attempt to replace a couple of variants
+of the `Namespace.CustomViewFoo`. One is the original casing found in the C# source
+files. The other is all lowercase. If we cannot find a match we will do a case 
+insensitive lookup to see if there are items which do match. If we find one this 
+error will be raised.
+
+We found a matching key 'Namespace.CustomViewFoo' for 'NameSpace.CustomViewFoo'. But the casing was incorrect. Please correct the casing

Documentation/guides/messages/xa1001.md

@@ -0,0 +1,7 @@
+# Compiler Warning XA1001
+
+AndroidResgen: Warning while updating Resource XML '{filename}': {Message}
+
+This warning is raised if we encounter an unknown issue when processing
+the layout and resources. It is a generic warning that does not describe 
+any specific problem. The details will be in the `{Message}`.