docs: Add notes about common acronyms (#8298)

include/xrpl/protocol/STLedgerEntry.h

@@ -22,6 +22,9 @@ namespace test {
 class InvariantsMisc_test;
 }  // namespace test
 
+/**
+ * A serialized ledger entry, commonly abbreviated "SLE".
+ */
 class STLedgerEntry final : public STObject, public CountedObject<STLedgerEntry>
 {
     uint256 key_;

src/test/jtx/Env.h

@@ -702,6 +702,7 @@ public:
     /**
      * Return an account root.
      * @return empty if the account does not exist.
+     * @note "le" stands for "ledger entry".
      */
     [[nodiscard]] SLE::const_pointer
     le(Account const& account) const;
@@ -709,6 +710,7 @@ public:
     /**
      * Return a ledger entry.
      * @return empty if the ledger entry does not exist
+     * @note "le" stands for "ledger entry".
      */
     [[nodiscard]] SLE::const_pointer
     le(Keylet const& k) const;