Extending cheat_sheet.md to ease dev

cheat_sheet.md

@@ -92,3 +92,90 @@
     ]
 }
 ```
+
+## category_tree.json 
+#### (not mandatory)
+
+```
+[
+  {
+    "children":[
+      {
+        "code":"ap",
+        "name":"Average Price Data"
+      },
+      {
+        "code":"cw",
+        "name":"Urban Wage Earners and Clerical Workers (Current Series)"
+      },
+      {
+        "code":"cu",
+        "name":"All Urban Consumers (Current Series)"
+      },
+      {
+        "code":"pc",
+        "name":"Industry Data"
+      },
+      {
+        "code":"wp",
+        "name":"Commodity Data including \"headline\" FD-ID indexes"
+      }
+    ],
+    "code":"inflation_and_prices",
+    "name":"Inflation & Prices"
+  },
+  {
+    "children":[
+      {
+        "code":"fm",
+        "name":"Marital and family labor force statistics"
+      },
+      {
+        "code":"lu",
+        "name":"Union Affiliation Data"
+      },
+      {
+        "code":"sm",
+        "name":"Employment, Hours, and Earnings - State and Metro Area"
+      }
+    ],
+    "code":"employment",
+    "name":"Employment"
+  },
+  {
+    "children":[
+      {
+        "code":"la",
+        "name":"Local Area Unemployment Statistics (LAUS)"
+      }
+    ],
+    "code":"unemployment",
+    "name":"Unemployment"
+  }
+  ]
+  ```
+
+  ## Observations.tsv 
+```
+PERIOD  VALUE
+2013    78
+2014    75.3
+
+```
+- Conventions for observations files
+    * File values must me SORTED in ASCENDING Values
+    * Remove M13 Q5 S3 W54 
+    * Add a `\n` at the end of the file
+    * Periods must be consistant and continous
+    * File an have an additionnal column
+
+- Conventions for PERIOD
+    - `YYYY` for years
+    - `YYYY-MM` for months (MUST be padded for `MM`)
+    - `YYYY-MM-DD` for days (MUST be padded for `MM` and `DD`)
+    - `YYYY-Q[1-4]` for year quarters
+    - `YYYY-S[1-2]` for year semesters
+    - `YYYY-W[01-53]` for year weeks (MUST be padded)
+- Conventions for VALUE
+    - decimal with `.`
+    - if value is blank write `NA`