Fix typo and grammar

Fix typo and grammar in the coin selection algorithm's description.

Author: Heebs

src/wallet/coinselection.cpp

@@ -26,7 +26,7 @@ struct {
  * set that can pay for the spending target and does not exceed the spending target by more than the
  * cost of creating and spending a change output. The algorithm uses a depth-first search on a binary
  * tree. In the binary tree, each node corresponds to the inclusion or the omission of a UTXO. UTXOs
- * are sorted by their effective values and the trees is explored deterministically per the inclusion
+ * are sorted by their effective values and the tree is explored deterministically per the inclusion
  * branch first. At each node, the algorithm checks whether the selection is within the target range.
  * While the selection has not reached the target range, more UTXOs are included. When a selection's
  * value exceeds the target range, the complete subtree deriving from this selection can be omitted.
@@ -36,7 +36,7 @@ struct {
  * The search continues to search for better solutions after one solution has been found. The best
  * solution is chosen by minimizing the waste metric. The waste metric is defined as the cost to
  * spend the current inputs at the given fee rate minus the long term expected cost to spend the
- * inputs, plus the amount the selection exceeds the spending target:
+ * inputs, plus the amount by which the selection exceeds the spending target:
  *
  * waste = selectionTotal - target + inputs × (currentFeeRate - longTermFeeRate)
  *