docs: update docs up to 0.5.9 features (#53)

# Rationale for this change
We need to update our docs as we introduce new features. 
<!--
Why are you proposing this change? If this is already explained clearly
in the linked Jira ticket then this section is not needed.
Explaining clearly why changes are proposed helps reviewers understand
your changes and offer better suggestions for fixes.
-->

# What changes are included in this PR?
- add timestamp to SQL spec
- add numerical operations & new datatypes to supported SQL syntax
<!--
There is no need to duplicate the description in the ticket here but it
is sometimes worth providing a summary of the individual changes in this
PR.
-->

# Are these changes tested?
N/A
<!--
We typically require tests for all PRs in order to:
1. Prevent the code from being accidentally broken by subsequent changes
2. Serve as another way to document the expected behavior of the code

If tests are not included in your PR, please explain why (for example,
are they covered by existing tests)?
-->

crates/proof-of-sql/README.md

@@ -171,8 +171,9 @@ See the [SQL specification](https://github.com/spaceandtimelabs/sxt-proof-of-sql
 * `GROUP BY`
 * Comparison operations: `=`, `>=`, `<=`, etc.
 * Logical operations: `AND`, `OR`, `NOT`.
+* Numerical operations `+`, `-`, `*`.
 * Aggregations: `SUM`, `COUNT`
-* Data Types: `BIGINT`, `VARCHAR`, `DECIMAL75`.
+* Data Types: `BOOLEAN`, Integer types, `VARCHAR`, `DECIMAL75`, `TIMESTAMP`.
 
 
 ## Roadmap

docs/SQLSyntaxSpecification.md

@@ -13,15 +13,17 @@ FROM table
 ```
 ## Supported in the Prover
 * DataTypes
-    - Boolean
+    - Bool / Boolean
     - Numeric Types
-        * SmallInt / Int16
-        * Int / Int32
-        * BigInt / Int64
+        * SmallInt (16 bits)
+        * Int / Integer (32 bits)
+        * BigInt (64 bits)
         * Int128
         * Decimal75
     - Character Types
         * Varchar [^1]
+    - Date / Time Types
+        * Timestamp
 * Operators
     - Logical Operators
         * AND, OR