[stable10] Point to current installation instructions in README

[phil-davis]

Backport #35036

Note: I including the 2nd commit from the master PR because it seems reasonable to just keep the README in stable10 pointing to the latest docs. Otherwise we have to remember to bump this with every minor version release. And actually people will anyway mostly use this link from the master branch on the default GitHub UI page.

[codecov]

Codecov Report

Merging #35037 into stable10 will decrease coverage by 0.26%.
The diff coverage is n/a.

@@              Coverage Diff               @@
##             stable10   #35037      +/-   ##
==============================================
- Coverage       64.46%   64.19%   -0.27%     
  Complexity      20064    20064              
==============================================
  Files            1286     1286              
  Lines           76928    76928              
  Branches         1307     1307              
==============================================
- Hits            49594    49387     -207     
- Misses          26953    27160     +207     
  Partials          381      381

Flag	Coverage Δ	Complexity Δ
#javascript	53.01% <ø> (ø)	0 <ø> (ø)	⬇️
#phpunit	65.38% <ø> (-0.3%)	20064 <ø> (ø)

Impacted Files	Coverage Δ	Complexity Δ
lib/private/DB/AdapterOCI8.php	0% <0%> (-86.67%)	4% <0%> (ø)
...Builder/ExpressionBuilder/OCIExpressionBuilder.php	0% <0%> (-85.19%)	18% <0%> (ø)
lib/private/DB/OracleMigrator.php	0% <0%> (-80.71%)	29% <0%> (ø)
lib/private/DB/OracleConnection.php	0% <0%> (-66.67%)	12% <0%> (ø)
lib/private/DB/Adapter.php	82.71% <0%> (-6.18%)	25% <0%> (ø)
lib/private/DB/ConnectionFactory.php	78.94% <0%> (-3.95%)	21% <0%> (ø)
lib/private/Repair/RepairMismatchFileCachePath.php	94.57% <0%> (-3.49%)	51% <0%> (ø)
lib/private/Repair/RepairInvalidShares.php	97.26% <0%> (-2.74%)	17% <0%> (ø)
lib/private/AllConfig.php	92.46% <0%> (-2.06%)	43% <0%> (ø)
lib/private/Files/Cache/Cache.php	95.82% <0%> (-1.8%)	110% <0%> (ø)
... and 4 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 27ada5c...364035c. Read the comment docs.

[codecov]

Codecov Report

Merging #35037 into stable10 will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             stable10   #35037   +/-   ##
===========================================
  Coverage       64.46%   64.46%           
  Complexity      20064    20064           
===========================================
  Files            1286     1286           
  Lines           76928    76928           
  Branches         1307     1307           
===========================================
  Hits            49594    49594           
  Misses          26953    26953           
  Partials          381      381

Flag	Coverage Δ	Complexity Δ
#javascript	53.01% <ø> (ø)	0 <ø> (ø)	⬇️
#phpunit	65.68% <ø> (ø)	20064 <ø> (ø)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 27ada5c...364035c. Read the comment docs.