docs: fix typos and improve grammar (#4961)

This pull request addresses several minor typos and grammatical
improvements across multiple documentation files.

### Changes made:
- Corrected the article "A" to "An" in the **pindexer README** file,
where it was incorrectly used before a word starting with a vowel sound.
- Fixed a spelling issue in the **spend_key.md** file, where
"organizational" was written without the hyphen.
- Updated the **routing.md** file to fix a similar article issue,
changing "a index" to "an index."
- Corrected missing hyphen in the compound adjective "right hand" in
**contributions.md**.

### Issue Ticket:
- No related ticket.

### Testing:
- Review the changes in the respective markdown files and ensure that
the grammar and spelling adjustments align with standard English
conventions.

### Checklist before requesting a review:
- [ ] I have added guiding text to explain how a reviewer should test
these changes.
- [ ] If this code contains consensus-breaking changes, I have added the
"consensus-breaking" label. Otherwise, I declare my belief that there
are not consensus-breaking changes.

---------

Signed-off-by: Dmytrol <[email protected]>

crates/bin/pindexer/README.md

@@ -1,6 +1,6 @@
 # pindexer
 
-A indexer that ingests ABCI events emitted by pd and transforms them into useful data.
+An indexer that ingests ABCI events emitted by pd and transforms them into useful data.
 
 ## Usage
 

docs/protocol/src/addresses_keys/spend_key.md

@@ -16,7 +16,7 @@ spend authority was derived using the salt `mnemonic0`.
 ## Default BIP44 Derivation
 
 Beginning in Testnet 62, from the mnemonic seed phrase, spend `seeds` were derived
-as described in [BIP44]. The BIP44 specification describes a organizational
+as described in [BIP44]. The BIP44 specification describes an organizational
 hierarchy allowing a user to remember a single seed phrase for multiple
 cryptocurrencies. 
 
@@ -79,4 +79,4 @@ check it.
 [BIP32]: https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki
 [BIP39]: https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki
 [BIP44]: https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki
-[SLIP-0044]: https://github.com/satoshilabs/slips/blob/master/slip-0044.md
+[SLIP-0044]: https://github.com/satoshilabs/slips/blob/master/slip-0044.md

docs/protocol/src/dex/routing.md

@@ -182,7 +182,7 @@ $\Lambda_2 = \Delta_1 \frac {p} {q \gamma}$
 
 Filling backward is more complicated because we need to ensure every position preceding the constraining hop is zeroed out. This is because the DEX engine only has access to a finite amount of precision and as a result perform division can be lossy by some $\epsilon$, perpetually preventing a position to be deindexed.
 
-Suppose that the limiting constraint is a index $j$, we compute $\Delta_1^* = \frac {p_2 \gamma} {p_1} R_2$
+Suppose that the limiting constraint is an index $j$, we compute $\Delta_1^* = \frac {p_2 \gamma} {p_1} R_2$
 
 The goal is to propagate rounding loss backwards to the input and forwards the output. That means that for a constraint at index $j$, we fill backward from $j$ to the first position, and forward from $j$ to the last position. For backward fills, we compute $\Delta_1^* = \Lambda_2 \frac {p_2 \gamma} {p_1}$ and manually zero-out the $R_2$ of each position. The forward fill part works as described previously. There is no extra work to do because that segment of the path contains no constraints as we have reduced the flow to match the exact capacity of the frontier.
 

docs/protocol/src/setup/contributions.md

@@ -171,7 +171,7 @@ Very often, we need to check equations of the form:
 $$
 \forall i.\ A_i \odot B = C \odot D_i
 $$
-(this would also work if the right hand side is of the form $D_i \odot C$, and vice versa).
+(this would also work if the right-hand side is of the form $D_i \odot C$, and vice versa).
 
 This equation is equivalent to checking:
 $$