Docs: three typos in README and docs/INSTALL.md (available/effect/documents)

[ishan-puri]

Hi team—found a few small doc typos:

1. README.md → “News” section (Jan 2022):

   • “More models are availabel.” → “More models are available.”

2. docs/INSTALL.md → Windows subsection:

   • “The affect is that models ended with '-dcn' is not supported.”
     → Suggest: “The effect is that models ending with '-dcn' are not supported.”
     (also improves subject–verb agreement)

3. docs/INSTALL.md → Models / tracking:

   • “tracking docments” → “tracking documents”

I searched open issues for these strings and didn’t find an existing report.
Happy to open a PR with fixes if you’d like. Thanks!