Add exemplar JSON mapping

# Why is the change needed?

This change introduces an exemplary tagset mapping for Neo-GATE in JSON format.
The file will be referenced in `README.md` to provide users with a starting point to create custom neomorpheme paradigm mappings to Neo-GATE's tagset.

# What changes does the patch introduce?

The patch adds the `schwa.json` file to the repository.

# How was this patch tested?

No tests are required.

schwa.json

@@ -0,0 +1,38 @@
+{
+    "<ENDS>": "ə",
+    "<ENDP>": "ɜ",
+    "<DARTS>": "lə",
+    "<DARTP>": "lɜ",
+    "<IART>": "unə",
+    "<PARTS>": "deə",
+    "<PARTP>": "deɜ",
+    "<PRON>": "ləi",
+    "<PREPdiS>": "dellə",
+    "<PREPdiP>": "dellɜ",
+    "<PREPaS>": "allə",
+    "<PREPaP>": "allɜ",
+    "<PREPdaS>": "dallə",
+    "<PREPdaP>": "dallɜ",
+    "<PREPinS>": "nellə",
+    "<PREPinP>": "nellɜ",
+    "<PREPsuS>": "sullə",
+    "<PREPsuP>": "sullɜ",
+    "<DADJquelS>": "quellə",
+    "<DADJquelP>": "quellɜ",
+    "<DADJquestS>": "questə",
+    "<DADJquestP>": "questɜ",
+    "<POSS1S>": "miə",
+    "<POSS1P>": "miɜ",
+    "<POSS2S>": "tuə",
+    "<POSS2P>": "tuɜ",
+    "<POSS3S>": "suə",
+    "<POSS3P>": "suɜ",
+    "<POSS4S>": "nostrə",
+    "<POSS4P>": "nostrɜ",
+    "<POSS5S>": "vostrə",
+    "<POSS5P>": "vostrɜ",
+    "<PRONDOBJS>": "lə",
+    "<PRONDOBJP>": "lɜ",
+    "<PRONIOBJS>": "lə",
+    "<PRONIOBJP>": "lɜ"
+  }