fix: typos and article usage in various documentation files (#1547)

This PR addresses multiple typos and fixes article usage errors across
several documentation files. The following changes were made:
- Replaced "an" with "a" where the following word does not start with a
vowel sound (e.g., "a user" instead of "an user").
- Added hyphen to "above-mentioned" to maintain proper spelling.
- Fixed phrasing for consistency and clarity in multiple sections.

Files updated:
- `adr-001-block-propagation.md`
- `adr-006-row-propagation.md`
- `adr-template.md`
- `pex.md`

These changes aim to improve readability and correctness in the
documentation.

docs/celestia-architecture/adr-001-block-propagation.md

@@ -102,7 +102,7 @@ When a user requests a block from the LL node, the request will be set to the IP
 
 ![user request flow](./assets/user-request.png)
 
-The goal is to not change the public interface for RPC's. It is yet to be seen if this possible. This means that CIDs will need to be set and loaded from the store in order to get all the related block information an user requires.
+The goal is to not change the public interface for RPC's. It is yet to be seen if this possible. This means that CIDs will need to be set and loaded from the store in order to get all the related block information a user requires.
 
 ## Status
 

docs/celestia-architecture/adr-006-row-propagation.md

@@ -69,7 +69,7 @@ decrease the number of required changes. Below, implementation semantics are pre
 // Row represents a blob of multiple ExtendedDataSquare shares.
 // Practically, it is half of an extended row, as other half can be recomputed.
 type Row struct {
-// Index is an top-to-bottom index of a Row in ExtendedDataSquare.
+// Index is a top-to-bottom index of a Row in ExtendedDataSquare.
 // NOTE: Row Index is unnecessary, as we can determine it's Index by hash from DAHeader. However, Index removal
 // would bring more changes to Consensus Reactor with arguable pros of less bandwidth usage.
 Index int
@@ -199,4 +199,4 @@ Proposed
     comparison. The actual data size in such a case for the Row would be 128x256(shares_per_row*share_size)=32KiB, which
     is exactly two times smaller than a Part.
 * Gossiped chunks are no longer constant size. Instead, their size is proportional to the size of Block's data.
-* Another step back from original Tendermint's codebases
+* Another step back from original Tendermint's codebases

docs/celestia-architecture/adr-template.md

@@ -10,7 +10,7 @@
 
 ## Alternative Approaches
 
-> This section contains information around alternative options that are considered before making a decision. It should contain a explanation on why the alternative approach(es) were not chosen.
+> This section contains information around alternative options that are considered before making a decision. It should contain an explanation on why the alternative approach(es) were not chosen.
 
 ## Decision